[sensors] Dispatch sensor events using postTask

In order to avoid re-entrancy issues, this CL modifies sensor event
dispatching code and uses postTask to schedule event dispatch.
New test is added to ambient-light-sensor.html that checks if generic
sensor code works correctly when sensor is not supported

BUG=606766

Review-Url: https://codereview.chromium.org/2381913002
Cr-Commit-Position: refs/heads/master@{#422761}

third_party/WebKit/LayoutTests/sensor/ambient-light-sensor.html

@@ -22,6 +22,19 @@ test(() => assert_throws(
     () => new AmbientLightSensor({frequency: -60})),
     'Test that negative frequency causes exception from constructor.');
 
+sensor_test(sensor => {
+  sensor.mockSensorProvider.setGetSensorShouldFail(true);
+  let ambientLightSensor = new AmbientLightSensor();
+  ambientLightSensor.start();
+  return new Promise((resolve, reject) => {
+    ambientLightSensor.onstatechange = event => {
+      if(ambientLightSensor.state == 'errored') {
+        resolve();
+      }
+    };
+  });
+}, 'Test that sensor state changes to "errored" when sensor is not supported.');
+
 sensor_test(sensor => {
   let ambientLightSensor = new AmbientLightSensor({frequency: 560});
   ambientLightSensor.start();

third_party/WebKit/LayoutTests/sensor/resources/sensor-helpers.js

@@ -194,7 +194,8 @@ function sensor_mocks(mojo) {
       // Returns initialized Sensor proxy to the client.
       getSensor(type, stub) {
         if (this.get_sensor_should_fail_) {
-          return getSensorResponse(null, null);
+          return getSensorResponse(null,
+              connection.bindProxy(null, sensor.SensorClient));
         }
 
         let offset =

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

@@ -6,6 +6,7 @@
 
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
+#include "core/dom/ExecutionContextTask.h"
 #include "core/inspector/ConsoleMessage.h"
 #include "device/generic_sensor/public/interfaces/sensor.mojom-blink.h"
 #include "modules/sensor/SensorErrorEvent.h"
@@ -268,9 +269,13 @@ void Sensor::pollForData() {
   m_sensorProxy->updateInternalReading();
 
   DCHECK(m_sensorReading);
-  if (m_sensorReading->isReadingUpdated(m_storedData))
-    dispatchEvent(
-        SensorReadingEvent::create(EventTypeNames::change, m_sensorReading));
+  if (getExecutionContext() &&
+      m_sensorReading->isReadingUpdated(m_storedData)) {
+    getExecutionContext()->postTask(
+        BLINK_FROM_HERE,
+        createSameThreadTask(&Sensor::notifySensorReadingChanged,
+                             wrapWeakPersistent(this)));
+  }
 
   m_storedData = m_sensorProxy->reading();
 }
@@ -279,7 +284,12 @@ void Sensor::updateState(Sensor::SensorState newState) {
   if (newState == m_state)
     return;
   m_state = newState;
-  dispatchEvent(Event::create(EventTypeNames::statechange));
+  if (getExecutionContext()) {
+    getExecutionContext()->postTask(
+        BLINK_FROM_HERE, createSameThreadTask(&Sensor::notifyStateChanged,
+                                              wrapWeakPersistent(this)));
+  }
+
   updatePollingStatus();
 }
 
@@ -300,4 +310,13 @@ void Sensor::updatePollingStatus() {
   }
 }
 
+void Sensor::notifySensorReadingChanged() {
+  dispatchEvent(
+      SensorReadingEvent::create(EventTypeNames::change, m_sensorReading));
+}
+
+void Sensor::notifyStateChanged() {
+  dispatchEvent(Event::create(EventTypeNames::statechange));
+}
+
 }  // namespace blink

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

@@ -102,6 +102,9 @@ class Sensor : public EventTargetWithInlineData,
 
   void updatePollingStatus();
 
+  void notifySensorReadingChanged();
+  void notifyStateChanged();
+
  private:
   Member<SensorReading> m_sensorReading;
   SensorOptions m_sensorOptions;