Revert of [Sensors] Align sensor reading updates and 'onchange' notification...

Revert of [Sensors] Align sensor reading updates and 'onchange' notification with rAF. (patchset #6 id:140001 of https://codereview.chromium.org/2551223003/ )

Reason for revert:
Seems like a likely cause for failures on:

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=sensor%2Faccelerometer.html&testType=webkit_tests

Original issue's description:
> [Sensors] Align sensor reading updates and 'onchange' notification with rAF.
>
> For all sensors new reading values are read and 'onchange' notfication is send from rAF callbacks, thus avoiding possible Critical Rendering Path interruption.
>
> Before this change a timers were used and this could unnecessarily drain CPU and battery.
>
> BUG=668052
> BUG=606766
>
> Committed: https://crrev.com/6b071fe7dc3bd64a2914eadd5c67b483d064a6cb
> Cr-Commit-Position: refs/heads/master@{#439467}

TBR=reillyg@chromium.org,alexander.shalamov@intel.com,haraken@chromium.org,foolip@chromium.org,mikhail.pozdnyakov@intel.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=668052

Review-Url: https://codereview.chromium.org/2590513002
Cr-Commit-Position: refs/heads/master@{#439487}

third_party/WebKit/LayoutTests/sensor/resources/generic-sensor-tests.js

@@ -304,10 +304,7 @@ function runGenericSensorTests(sensorType, updateReading, verifyReading) {
                 // By the moment slow sensor (9 Hz) is notified for the
                 // next time, the fast sensor (30 Hz) has been notified
                 // for int(30/9) = 3 times.
-                // In actual implementation updates are bound to rAF,
-                // (not to a timer) sometimes fast sensor gets invoked 4 times.
-                assert_true(fastSensorNotifiedCounter == 3 ||
-                            fastSensorNotifiedCounter == 4);
+                assert_equals(fastSensorNotifiedCounter, 3);
                 fastSensor.stop();
                 slowSensor.stop();
                 resolve(mockSensor);

third_party/WebKit/Source/modules/sensor/BUILD.gn

@@ -32,8 +32,8 @@ blink_modules_sources("sensor") {
     "SensorProxy.h",
     "SensorReading.cpp",
     "SensorReading.h",
-    "SensorReadingUpdater.cpp",
-    "SensorReadingUpdater.h",
+    "SensorUpdateNotificationStrategy.cpp",
+    "SensorUpdateNotificationStrategy.h",
   ]
 
   deps = [

third_party/WebKit/Source/modules/sensor/Sensor.cpp

@@ -13,6 +13,7 @@
 #include "modules/sensor/SensorErrorEvent.h"
 #include "modules/sensor/SensorProviderProxy.h"
 #include "modules/sensor/SensorReading.h"
+#include "modules/sensor/SensorUpdateNotificationStrategy.h"
 
 using namespace device::mojom::blink;
 
@@ -25,8 +26,7 @@ Sensor::Sensor(ExecutionContext* executionContext,
     : ContextLifecycleObserver(executionContext),
       m_sensorOptions(sensorOptions),
       m_type(type),
-      m_state(Sensor::SensorState::Idle),
-      m_lastUpdateTimestamp(0.0) {
+      m_state(Sensor::SensorState::Idle) {
   // Check secure context.
   String errorMessage;
   if (!executionContext->isSecureContext(errorMessage)) {
@@ -164,7 +164,7 @@ void Sensor::initSensorProxyIfNeeded() {
   m_sensorProxy = provider->getSensorProxy(m_type);
 
   if (!m_sensorProxy) {
-    m_sensorProxy = provider->createSensorProxy(m_type, document,
+    m_sensorProxy = provider->createSensorProxy(m_type, document->page(),
                                                 createSensorReadingFactory());
   }
 }
@@ -182,15 +182,10 @@ void Sensor::onSensorInitialized() {
   startListening();
 }
 
-void Sensor::onSensorReadingChanged(double timestamp) {
-  if (m_state != Sensor::SensorState::Activated)
-    return;
-
-  DCHECK_GT(m_configuration->frequency, 0.0);
-  double period = 1 / m_configuration->frequency;
-  if (timestamp - m_lastUpdateTimestamp >= period) {
-    m_lastUpdateTimestamp = timestamp;
-    notifySensorReadingChanged();
+void Sensor::onSensorReadingChanged() {
+  if (m_state == Sensor::SensorState::Activated) {
+    DCHECK(m_sensorUpdateNotifier);
+    m_sensorUpdateNotifier->onSensorReadingChanged();
   }
 }
 
@@ -198,6 +193,8 @@ void Sensor::onSensorError(ExceptionCode code,
                            const String& sanitizedMessage,
                            const String& unsanitizedMessage) {
   reportError(code, sanitizedMessage, unsanitizedMessage);
+  if (m_sensorUpdateNotifier)
+    m_sensorUpdateNotifier->cancelPendingNotifications();
 }
 
 void Sensor::onStartRequestCompleted(bool result) {
@@ -211,6 +208,13 @@ void Sensor::onStartRequestCompleted(bool result) {
     return;
   }
 
+  DCHECK(m_configuration);
+  DCHECK(m_sensorProxy);
+  auto updateCallback =
+      WTF::bind(&Sensor::onSensorUpdateNotification, wrapWeakPersistent(this));
+  DCHECK_GT(m_configuration->frequency, 0);
+  m_sensorUpdateNotifier = SensorUpdateNotificationStrategy::create(
+      m_configuration->frequency, std::move(updateCallback));
   updateState(Sensor::SensorState::Activated);
 }
 
@@ -241,6 +245,9 @@ void Sensor::stopListening() {
   DCHECK(m_sensorProxy);
   updateState(Sensor::SensorState::Idle);
 
+  if (m_sensorUpdateNotifier)
+    m_sensorUpdateNotifier->cancelPendingNotifications();
+
   if (m_sensorProxy->isInitialized()) {
     DCHECK(m_configuration);
     m_sensorProxy->removeConfiguration(m_configuration->Clone());
@@ -248,6 +255,25 @@ void Sensor::stopListening() {
   m_sensorProxy->removeObserver(this);
 }
 
+void Sensor::onSensorUpdateNotification() {
+  if (m_state != Sensor::SensorState::Activated)
+    return;
+
+  DCHECK(m_sensorProxy);
+  DCHECK(m_sensorProxy->isInitialized());
+  DCHECK(m_sensorProxy->sensorReading());
+
+  if (getExecutionContext() &&
+      m_sensorProxy->sensorReading()->isReadingUpdated(m_storedData)) {
+    getExecutionContext()->postTask(
+        TaskType::Sensor, BLINK_FROM_HERE,
+        createSameThreadTask(&Sensor::notifySensorReadingChanged,
+                             wrapWeakPersistent(this)));
+  }
+
+  m_storedData = m_sensorProxy->sensorReading()->data();
+}
+
 void Sensor::updateState(Sensor::SensorState newState) {
   if (newState == m_state)
     return;
@@ -277,14 +303,13 @@ void Sensor::reportError(ExceptionCode code,
   }
 }
 
-void Sensor::notifySensorReadingChanged() {
-  DCHECK(m_sensorProxy);
-  DCHECK(m_sensorProxy->sensorReading());
+void Sensor::onSuspended() {
+  if (m_sensorUpdateNotifier)
+    m_sensorUpdateNotifier->cancelPendingNotifications();
+}
 
-  if (m_sensorProxy->sensorReading()->isReadingUpdated(m_storedData)) {
-    m_storedData = m_sensorProxy->sensorReading()->data();
-    dispatchEvent(Event::create(EventTypeNames::change));
-  }
+void Sensor::notifySensorReadingChanged() {
+  dispatchEvent(Event::create(EventTypeNames::change));
 }
 
 void Sensor::notifyOnActivate() {

third_party/WebKit/Source/modules/sensor/Sensor.h

@@ -20,6 +20,7 @@ namespace blink {
 class ExceptionState;
 class ExecutionContext;
 class SensorReading;
+class SensorUpdateNotificationStrategy;
 
 class Sensor : public EventTargetWithInlineData,
                public ActiveScriptWrappable<Sensor>,
@@ -82,10 +83,11 @@ class Sensor : public EventTargetWithInlineData,
 
   // SensorController::Observer overrides.
   void onSensorInitialized() override;
-  void onSensorReadingChanged(double timestamp) override;
+  void onSensorReadingChanged() override;
   void onSensorError(ExceptionCode,
                      const String& sanitizedMessage,
                      const String& unsanitizedMessage) override;
+  void onSuspended() override;
 
   void onStartRequestCompleted(bool);
   void onStopRequestCompleted(bool);
@@ -93,6 +95,8 @@ class Sensor : public EventTargetWithInlineData,
   void startListening();
   void stopListening();
 
+  void onSensorUpdateNotification();
+
   void updateState(SensorState newState);
   void reportError(ExceptionCode = UnknownError,
                    const String& sanitizedMessage = String(),
@@ -107,9 +111,9 @@ class Sensor : public EventTargetWithInlineData,
   device::mojom::blink::SensorType m_type;
   SensorState m_state;
   Member<SensorProxy> m_sensorProxy;
+  std::unique_ptr<SensorUpdateNotificationStrategy> m_sensorUpdateNotifier;
   device::SensorReading m_storedData;
   SensorConfigurationPtr m_configuration;
-  double m_lastUpdateTimestamp;
 };
 
 }  // namespace blink

third_party/WebKit/Source/modules/sensor/SensorProviderProxy.cpp

@@ -55,12 +55,12 @@ DEFINE_TRACE(SensorProviderProxy) {
 
 SensorProxy* SensorProviderProxy::createSensorProxy(
     device::mojom::blink::SensorType type,
-    Document* document,
+    Page* page,
     std::unique_ptr<SensorReadingFactory> readingFactory) {
   DCHECK(!getSensorProxy(type));
 
   SensorProxy* sensor =
-      new SensorProxy(type, this, document, std::move(readingFactory));
+      new SensorProxy(type, this, page, std::move(readingFactory));
   m_sensorProxies.add(sensor);
 
   return sensor;

third_party/WebKit/Source/modules/sensor/SensorProviderProxy.h

@@ -13,7 +13,7 @@
 
 namespace blink {
 
-class Document;
+class Page;
 class SensorProxy;
 class SensorReadingFactory;
 
@@ -31,7 +31,7 @@ class SensorProviderProxy final
   ~SensorProviderProxy();
 
   SensorProxy* createSensorProxy(device::mojom::blink::SensorType,
-                                 Document*,
+                                 Page*,
                                  std::unique_ptr<SensorReadingFactory>);
 
   SensorProxy* getSensorProxy(device::mojom::blink::SensorType);

third_party/WebKit/Source/modules/sensor/SensorProxy.cpp

@@ -4,11 +4,9 @@
 
 #include "modules/sensor/SensorProxy.h"
 
-#include "core/dom/Document.h"
 #include "core/frame/LocalFrame.h"
 #include "modules/sensor/SensorProviderProxy.h"
 #include "modules/sensor/SensorReading.h"
-#include "modules/sensor/SensorReadingUpdater.h"
 #include "platform/mojo/MojoHelper.h"
 #include "public/platform/Platform.h"
 
@@ -18,18 +16,18 @@ namespace blink {
 
 SensorProxy::SensorProxy(SensorType sensorType,
                          SensorProviderProxy* provider,
-                         Document* document,
+                         Page* page,
                          std::unique_ptr<SensorReadingFactory> readingFactory)
-    : PageVisibilityObserver(document->page()),
+    : PageVisibilityObserver(page),
       m_type(sensorType),
       m_mode(ReportingMode::CONTINUOUS),
       m_provider(provider),
       m_clientBinding(this),
       m_state(SensorProxy::Uninitialized),
       m_suspended(false),
-      m_document(document),
       m_readingFactory(std::move(readingFactory)),
-      m_maximumFrequency(0.0) {}
+      m_maximumFrequency(0.0),
+      m_timer(this, &SensorProxy::onTimerFired) {}
 
 SensorProxy::~SensorProxy() {}
 
@@ -38,8 +36,6 @@ void SensorProxy::dispose() {
 }
 
 DEFINE_TRACE(SensorProxy) {
-  visitor->trace(m_document);
-  visitor->trace(m_readingUpdater);
   visitor->trace(m_reading);
   visitor->trace(m_observers);
   visitor->trace(m_provider);
@@ -71,10 +67,6 @@ void SensorProxy::initialize() {
                                              callback);
 }
 
-bool SensorProxy::isActive() const {
-  return isInitialized() && !m_suspended && !m_frequenciesUsed.isEmpty();
-}
-
 void SensorProxy::addConfiguration(
     SensorConfigurationPtr configuration,
     std::unique_ptr<Function<void(bool)>> callback) {
@@ -101,6 +93,12 @@ void SensorProxy::suspend() {
 
   m_sensor->Suspend();
   m_suspended = true;
+
+  if (usesPollingTimer())
+    updatePollingStatus();
+
+  for (Observer* observer : m_observers)
+    observer->onSuspended();
 }
 
 void SensorProxy::resume() {
@@ -111,8 +109,8 @@ void SensorProxy::resume() {
   m_sensor->Resume();
   m_suspended = false;
 
-  if (isActive())
-    m_readingUpdater->start();
+  if (usesPollingTimer())
+    updatePollingStatus();
 }
 
 const SensorConfiguration* SensorProxy::defaultConfig() const {
@@ -120,6 +118,10 @@ const SensorConfiguration* SensorProxy::defaultConfig() const {
   return m_defaultConfig.get();
 }
 
+bool SensorProxy::usesPollingTimer() const {
+  return isInitialized() && (m_mode == ReportingMode::CONTINUOUS);
+}
+
 void SensorProxy::updateSensorReading() {
   DCHECK(isInitialized());
   DCHECK(m_readingFactory);
@@ -134,14 +136,9 @@ void SensorProxy::updateSensorReading() {
   }
 
   m_reading = m_readingFactory->createSensorReading(readingData);
-}
 
-void SensorProxy::notifySensorChanged(double timestamp) {
-  // This notification leads to sync 'onchange' event sending, so
-  // we must cache m_observers as it can be modified within event handlers.
-  auto copy = m_observers;
-  for (Observer* observer : copy)
-    observer->onSensorReadingChanged(timestamp);
+  for (Observer* observer : m_observers)
+    observer->onSensorReadingChanged();
 }
 
 void SensorProxy::RaiseError() {
@@ -150,8 +147,7 @@ void SensorProxy::RaiseError() {
 
 void SensorProxy::SensorReadingChanged() {
   DCHECK_EQ(ReportingMode::ON_CHANGE, m_mode);
-  if (isActive())
-    m_readingUpdater->start();
+  updateSensorReading();
 }
 
 void SensorProxy::pageVisibilityChanged() {
@@ -173,9 +169,12 @@ void SensorProxy::handleSensorError(ExceptionCode code,
     return;
   }
 
-  m_state = Uninitialized;
-  m_frequenciesUsed.clear();
+  if (usesPollingTimer()) {  // Stop polling.
+    m_frequenciesUsed.clear();
+    updatePollingStatus();
+  }
 
+  m_state = Uninitialized;
   // The m_sensor.reset() will release all callbacks and its bound parameters,
   // therefore, handleSensorError accepts messages by value.
   m_sensor.reset();
@@ -229,10 +228,7 @@ void SensorProxy::onSensorCreated(SensorInitParamsPtr params,
   m_sensor.set_connection_error_handler(
       convertToBaseCallback(std::move(errorCallback)));
 
-  m_readingUpdater = SensorReadingUpdater::create(this, m_mode);
-
   m_state = Initialized;
-
   for (Observer* observer : m_observers)
     observer->onSensorInitialized();
 }
@@ -241,11 +237,9 @@ void SensorProxy::onAddConfigurationCompleted(
     double frequency,
     std::unique_ptr<Function<void(bool)>> callback,
     bool result) {
-  if (result) {
+  if (usesPollingTimer() && result) {
     m_frequenciesUsed.append(frequency);
-    std::sort(m_frequenciesUsed.begin(), m_frequenciesUsed.end());
-    if (isActive())
-      m_readingUpdater->start();
+    updatePollingStatus();
   }
 
   (*callback)(result);
@@ -256,6 +250,9 @@ void SensorProxy::onRemoveConfigurationCompleted(double frequency,
   if (!result)
     DVLOG(1) << "Failure at sensor configuration removal";
 
+  if (!usesPollingTimer())
+    return;
+
   size_t index = m_frequenciesUsed.find(frequency);
   if (index == kNotFound) {
     // Could happen e.g. if 'handleSensorError' was called before.
@@ -263,6 +260,7 @@ void SensorProxy::onRemoveConfigurationCompleted(double frequency,
   }
 
   m_frequenciesUsed.remove(index);
+  updatePollingStatus();
 }
 
 bool SensorProxy::tryReadFromBuffer(device::SensorReading& result) {
@@ -278,4 +276,28 @@ bool SensorProxy::tryReadFromBuffer(device::SensorReading& result) {
   return true;
 }
 
+void SensorProxy::updatePollingStatus() {
+  DCHECK(usesPollingTimer());
+
+  if (m_suspended || m_frequenciesUsed.isEmpty()) {
+    m_timer.stop();
+    return;
+  }
+  // TODO(Mikhail): Consider using sorted queue instead of searching
+  // max element each time.
+  auto it =
+      std::max_element(m_frequenciesUsed.begin(), m_frequenciesUsed.end());
+  DCHECK_GT(*it, 0.0);
+
+  double repeatInterval = 1 / *it;
+  if (!m_timer.isActive() || m_timer.repeatInterval() != repeatInterval) {
+    updateSensorReading();
+    m_timer.startRepeating(repeatInterval, BLINK_FROM_HERE);
+  }
+}
+
+void SensorProxy::onTimerFired(TimerBase*) {
+  updateSensorReading();
+}
+
 }  // namespace blink

third_party/WebKit/Source/modules/sensor/SensorProxy.h

@@ -12,6 +12,7 @@
 #include "device/generic_sensor/public/interfaces/sensor_provider.mojom-blink.h"
 #include "mojo/public/cpp/bindings/binding.h"
 #include "platform/Supplementable.h"
+#include "platform/Timer.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Vector.h"
 
@@ -20,7 +21,6 @@ namespace blink {
 class SensorProviderProxy;
 class SensorReading;
 class SensorReadingFactory;
-class SensorReadingUpdater;
 
 // This class wraps 'Sensor' mojo interface and used by multiple
 // JS sensor instances of the same type (within a single frame).
@@ -38,16 +38,13 @@ class SensorProxy final : public GarbageCollectedFinalized<SensorProxy>,
     // methods can be called.
     virtual void onSensorInitialized() {}
     // Platfrom sensort reading has changed.
-    // |timestamp| Reference timestamp in seconds of the moment when
-    // sensor reading was updated from the buffer.
-    // Note: |timestamp| values are only used to calculate elapsed time
-    // between shared buffer readings. These values *do not* correspond
-    // to sensor reading timestamps which are obtained on platform side.
-    virtual void onSensorReadingChanged(double timestamp) {}
+    virtual void onSensorReadingChanged() {}
     // An error has occurred.
     virtual void onSensorError(ExceptionCode,
                                const String& sanitizedMessage,
                                const String& unsanitizedMessage) {}
+    // Sensor reading change notification is suspended.
+    virtual void onSuspended() {}
   };
 
   ~SensorProxy();
@@ -62,10 +59,6 @@ class SensorProxy final : public GarbageCollectedFinalized<SensorProxy>,
   bool isInitializing() const { return m_state == Initializing; }
   bool isInitialized() const { return m_state == Initialized; }
 
-  // Is watching new reading data (initialized, not suspended and has
-  // configurations added).
-  bool isActive() const;
-
   void addConfiguration(device::mojom::blink::SensorConfigurationPtr,
                         std::unique_ptr<Function<void(bool)>>);
 
@@ -86,25 +79,20 @@ class SensorProxy final : public GarbageCollectedFinalized<SensorProxy>,
 
   double maximumFrequency() const { return m_maximumFrequency; }
 
-  Document* document() const { return m_document; }
-  const WTF::Vector<double>& frequenciesUsed() const {
-    return m_frequenciesUsed;
-  }
-
   DECLARE_VIRTUAL_TRACE();
 
  private:
   friend class SensorProviderProxy;
-  friend class SensorReadingUpdaterContinuous;
-  friend class SensorReadingUpdaterOnChange;
   SensorProxy(device::mojom::blink::SensorType,
               SensorProviderProxy*,
-              Document*,
+              Page*,
               std::unique_ptr<SensorReadingFactory>);
+  // Returns true if this instance is using polling timer to
+  // periodically fetch reading data from shared buffer.
+  bool usesPollingTimer() const;
 
   // Updates sensor reading from shared buffer.
   void updateSensorReading();
-  void notifySensorChanged(double timestamp);
 
   // device::mojom::blink::SensorClient overrides.
   void RaiseError() override;
@@ -128,7 +116,8 @@ class SensorProxy final : public GarbageCollectedFinalized<SensorProxy>,
   void onRemoveConfigurationCompleted(double frequency, bool result);
 
   bool tryReadFromBuffer(device::SensorReading& result);
-  void onAnimationFrame(double timestamp);
+  void updatePollingStatus();
+  void onTimerFired(TimerBase*);
 
   device::mojom::blink::SensorType m_type;
   device::mojom::blink::ReportingMode m_mode;
@@ -145,14 +134,13 @@ class SensorProxy final : public GarbageCollectedFinalized<SensorProxy>,
   mojo::ScopedSharedBufferHandle m_sharedBufferHandle;
   mojo::ScopedSharedBufferMapping m_sharedBuffer;
   bool m_suspended;
-  Member<Document> m_document;
   Member<SensorReading> m_reading;
   std::unique_ptr<SensorReadingFactory> m_readingFactory;
   double m_maximumFrequency;
 
-  Member<SensorReadingUpdater> m_readingUpdater;
+  // Used for continious reporting mode.
+  Timer<SensorProxy> m_timer;
   WTF::Vector<double> m_frequenciesUsed;
-  double m_lastRafTimestamp;
 
   using ReadingBuffer = device::SensorReadingSharedBuffer;
   static_assert(

third_party/WebKit/Source/modules/sensor/SensorReadingUpdater.cpp

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "modules/sensor/SensorReadingUpdater.h"
-
-#include "core/dom/Document.h"
-#include "device/generic_sensor/public/interfaces/sensor.mojom-blink.h"
-#include "modules/sensor/SensorProxy.h"
-#include "wtf/CurrentTime.h"
-
-using device::mojom::blink::ReportingMode;
-
-namespace blink {
-
-SensorReadingUpdater::SensorReadingUpdater(SensorProxy* sensorProxy)
-    : m_sensorProxy(sensorProxy), m_hasPendingAnimationFrameTask(false) {}
-
-void SensorReadingUpdater::enqueueAnimationFrameTask() {
-  if (m_hasPendingAnimationFrameTask)
-    return;
-
-  auto callback = WTF::bind(&SensorReadingUpdater::onAnimationFrame,
-                            wrapWeakPersistent(this));
-  m_sensorProxy->document()->enqueueAnimationFrameTask(std::move(callback));
-  m_hasPendingAnimationFrameTask = true;
-}
-
-void SensorReadingUpdater::start() {
-  enqueueAnimationFrameTask();
-}
-
-void SensorReadingUpdater::onAnimationFrame() {
-  m_hasPendingAnimationFrameTask = false;
-  onAnimationFrameInternal();
-}
-
-DEFINE_TRACE(SensorReadingUpdater) {
-  visitor->trace(m_sensorProxy);
-}
-
-class SensorReadingUpdaterContinuous : public SensorReadingUpdater {
- public:
-  explicit SensorReadingUpdaterContinuous(SensorProxy* sensorProxy)
-      : SensorReadingUpdater(sensorProxy) {}
-
-  DEFINE_INLINE_VIRTUAL_TRACE() { SensorReadingUpdater::trace(visitor); }
-
- protected:
-  void onAnimationFrameInternal() override {
-    if (!m_sensorProxy->isActive())
-      return;
-
-    m_sensorProxy->updateSensorReading();
-    m_sensorProxy->notifySensorChanged(WTF::monotonicallyIncreasingTime());
-    enqueueAnimationFrameTask();
-  }
-};
-
-// New data is fetched from shared buffer only once after 'start()'
-// call. Further, notification is send until every client is updated
-// (i.e. until longest notification period elapses) rAF stops after that.
-class SensorReadingUpdaterOnChange : public SensorReadingUpdater {
- public:
-  explicit SensorReadingUpdaterOnChange(SensorProxy* sensorProxy)
-      : SensorReadingUpdater(sensorProxy),
-        m_newDataArrivedTime(0.0),
-        m_newDataArrived(false) {}
-
-  DEFINE_INLINE_VIRTUAL_TRACE() { SensorReadingUpdater::trace(visitor); }
-
-  void start() override {
-    m_newDataArrived = true;
-    SensorReadingUpdater::start();
-  }
-
- protected:
-  void onAnimationFrameInternal() override {
-    if (!m_sensorProxy->isActive())
-      return;
-
-    double timestamp = WTF::monotonicallyIncreasingTime();
-
-    if (m_newDataArrived) {
-      m_newDataArrived = false;
-      m_sensorProxy->updateSensorReading();
-      m_newDataArrivedTime = timestamp;
-    }
-    m_sensorProxy->notifySensorChanged(timestamp);
-
-    DCHECK_GT(m_sensorProxy->frequenciesUsed().front(), 0.0);
-    double longestNotificationPeriod =
-        1 / m_sensorProxy->frequenciesUsed().front();
-
-    if (timestamp - m_newDataArrivedTime <= longestNotificationPeriod)
-      enqueueAnimationFrameTask();
-  }
-
- private:
-  double m_newDataArrivedTime;
-  bool m_newDataArrived;
-};
-
-// static
-SensorReadingUpdater* SensorReadingUpdater::create(SensorProxy* proxy,
-                                                   ReportingMode mode) {
-  if (mode == ReportingMode::CONTINUOUS)
-    return new SensorReadingUpdaterContinuous(proxy);
-  return new SensorReadingUpdaterOnChange(proxy);
-}
-
-}  // namespace blink

third_party/WebKit/Source/modules/sensor/SensorReadingUpdater.h

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef SensorReadingUpdater_h
-#define SensorReadingUpdater_h
-
-#include "device/generic_sensor/public/interfaces/sensor_provider.mojom-blink.h"
-#include "platform/heap/Handle.h"
-
-namespace blink {
-
-class SensorProxy;
-
-// This class encapsulates sensor reading update notification logic.
-class SensorReadingUpdater : public GarbageCollected<SensorProxy> {
- public:
-  static SensorReadingUpdater* create(SensorProxy*,
-                                      device::mojom::blink::ReportingMode);
-
-  virtual void start();
-
-  DECLARE_VIRTUAL_TRACE();
-
- protected:
-  explicit SensorReadingUpdater(SensorProxy*);
-  void enqueueAnimationFrameTask();
-  virtual void onAnimationFrameInternal() = 0;
-
-  Member<SensorProxy> m_sensorProxy;
-  bool m_hasPendingAnimationFrameTask;
-
- private:
-  void onAnimationFrame();
-};
-
-}  // namespace blink
-
-#endif  // SensorReadingUpdater_h

third_party/WebKit/Source/modules/sensor/SensorUpdateNotificationStrategy.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "modules/sensor/SensorUpdateNotificationStrategy.h"
+
+#include "device/generic_sensor/public/interfaces/sensor.mojom-blink.h"
+#include "platform/Timer.h"
+#include "wtf/CurrentTime.h"
+
+namespace blink {
+
+// Polls the buffer on signal from platform but not more frequently
+// than the given 'pollingPeriod'.
+class SensorUpdateNotificationStrategyImpl
+    : public SensorUpdateNotificationStrategy {
+ public:
+  SensorUpdateNotificationStrategyImpl(double frequency,
+                                       std::unique_ptr<Function<void()>> func)
+      : m_pollingPeriod(1 / frequency),
+        m_func(std::move(func)),
+        m_timer(this, &SensorUpdateNotificationStrategyImpl::onTimer),
+        m_lastPollingTimestamp(0.0) {
+    DCHECK_GT(frequency, 0.0);
+    DCHECK(m_func);
+  }
+
+ private:
+  // SensorUpdateNotificationStrategy overrides.
+  void onSensorReadingChanged() override;
+  void cancelPendingNotifications() override;
+
+  void onTimer(TimerBase*);
+  void notifyUpdate();
+
+  double m_pollingPeriod;
+  std::unique_ptr<Function<void()>> m_func;
+  Timer<SensorUpdateNotificationStrategyImpl> m_timer;
+  double m_lastPollingTimestamp;
+};
+
+void SensorUpdateNotificationStrategyImpl::onSensorReadingChanged() {
+  if (m_timer.isActive())
+    return;  // Skipping changes if update notification was already sheduled.
+
+  double elapsedTime =
+      WTF::monotonicallyIncreasingTime() - m_lastPollingTimestamp;
+
+  double waitingTime = m_pollingPeriod - elapsedTime;
+  const double minInterval =
+      1 / device::mojom::blink::SensorConfiguration::kMaxAllowedFrequency;
+
+  // Negative or zero 'waitingTime' means that polling period has elapsed.
+  // We also avoid scheduling if the elapsed time is slightly behind the
+  // polling period.
+  if (waitingTime < minInterval) {
+    notifyUpdate();
+  } else {
+    m_timer.startOneShot(waitingTime, BLINK_FROM_HERE);
+  }
+}
+
+void SensorUpdateNotificationStrategyImpl::cancelPendingNotifications() {
+  m_timer.stop();
+}
+
+void SensorUpdateNotificationStrategyImpl::notifyUpdate() {
+  m_lastPollingTimestamp = WTF::monotonicallyIncreasingTime();
+  (*m_func)();
+}
+
+void SensorUpdateNotificationStrategyImpl::onTimer(TimerBase*) {
+  notifyUpdate();
+}
+
+// static
+std::unique_ptr<SensorUpdateNotificationStrategy>
+SensorUpdateNotificationStrategy::create(
+    double pollingPeriod,
+    std::unique_ptr<Function<void()>> func) {
+  return std::unique_ptr<SensorUpdateNotificationStrategy>(
+      new SensorUpdateNotificationStrategyImpl(pollingPeriod, std::move(func)));
+}
+
+}  // namespace blink

third_party/WebKit/Source/modules/sensor/SensorUpdateNotificationStrategy.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SensorUpdateNotificationStrategy_h
+#define SensorUpdateNotificationStrategy_h
+
+#include "wtf/Functional.h"
+
+namespace blink {
+
+// This class encapsulates sensor reading update notification logic:
+// the callback is invoked after client calls 'onSensorReadingChanged()'
+// however considering the given sample frequency:
+// guaranteed not to be called more often than expected.
+class SensorUpdateNotificationStrategy {
+ public:
+  static std::unique_ptr<SensorUpdateNotificationStrategy> create(
+      double frequency,
+      std::unique_ptr<Function<void()>>);
+
+  virtual void onSensorReadingChanged() = 0;
+  virtual void cancelPendingNotifications() = 0;
+  virtual ~SensorUpdateNotificationStrategy() {}
+};
+
+}  // namespace blink
+
+#endif  // SensorUpdateNotificationStrategy_h