Add use counter for document level wheel event listeners.

This cl adds use counters to find out the ratio of the web pages that
add document level wheel event listeners with passive:false, true, or
unspecified. It also counts the number of document level wheel event
listeners with passive:unspecified that preventDefault wheel events.

This information is useful to investigate the potential performance
benefits and risks of changing the default value of the passive option
to be true for document level wheel/mousewheel event listeners.

Bug: 626196
Change-Id: Ib0ee64b1a5085813d9b70073747ec3f544fbb660
Reviewed-on: https://chromium-review.googlesource.com/1148783
Commit-Queue: Sahel Sharify <sahel@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578695}

third_party/blink/public/platform/web_feature.mojom

@@ -1974,6 +1974,10 @@ enum WebFeature {
   kV8RTCRtpTransceiver_Direction_AttributeSetter = 2515,
   kHTMLLinkElementDisabledByParser = 2516,
   kRequestIsHistoryNavigation = 2517,
+  kAddDocumentLevelPassiveTrueWheelEventListener = 2518,
+  kAddDocumentLevelPassiveFalseWheelEventListener = 2519,
+  kAddDocumentLevelPassiveDefaultWheelEventListener = 2520,
+  kDocumentLevelPassiveDefaultEventListenerPreventedWheel = 2521,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

third_party/blink/renderer/core/dom/events/event_target.cc

@@ -97,10 +97,14 @@ bool IsTouchScrollBlockingEvent(const AtomicString& event_type) {
          event_type == EventTypeNames::touchmove;
 }
 
+bool IsWheelScrollBlockingEvent(const AtomicString& event_type) {
+  return event_type == EventTypeNames::mousewheel ||
+         event_type == EventTypeNames::wheel;
+}
+
 bool IsScrollBlockingEvent(const AtomicString& event_type) {
   return IsTouchScrollBlockingEvent(event_type) ||
-         event_type == EventTypeNames::mousewheel ||
-         event_type == EventTypeNames::wheel;
+         IsWheelScrollBlockingEvent(event_type);
 }
 
 bool IsInstrumentedForAsyncStack(const AtomicString& event_type) {
@@ -208,6 +212,22 @@ inline LocalDOMWindow* EventTarget::ExecutingWindow() {
   return nullptr;
 }
 
+bool EventTarget::IsTopLevelNode() {
+  if (ToLocalDOMWindow())
+    return true;
+
+  Node* node = ToNode();
+  if (!node)
+    return false;
+
+  if (node->IsDocumentNode() || node->GetDocument().documentElement() == node ||
+      node->GetDocument().body() == node) {
+    return true;
+  }
+
+  return false;
+}
+
 void EventTarget::SetDefaultAddEventListenerOptions(
     const AtomicString& event_type,
     EventListener* event_listener,
@@ -232,19 +252,25 @@ void EventTarget::SetDefaultAddEventListenerOptions(
 
   if (RuntimeEnabledFeatures::PassiveDocumentEventListenersEnabled() &&
       IsTouchScrollBlockingEvent(event_type)) {
-    if (!options.hasPassive()) {
-      if (Node* node = ToNode()) {
-        if (node->IsDocumentNode() ||
-            node->GetDocument().documentElement() == node ||
-            node->GetDocument().body() == node) {
-          options.setPassive(true);
-          options.SetPassiveForcedForDocumentTarget(true);
-          return;
-        }
-      } else if (ToLocalDOMWindow()) {
-        options.setPassive(true);
-        options.SetPassiveForcedForDocumentTarget(true);
-        return;
+    if (!options.hasPassive() && IsTopLevelNode()) {
+      options.setPassive(true);
+      options.SetPassiveForcedForDocumentTarget(true);
+      return;
+    }
+  }
+
+  if (IsWheelScrollBlockingEvent(event_type) && IsTopLevelNode()) {
+    if (executing_window) {
+      if (options.hasPassive()) {
+        UseCounter::Count(
+            executing_window->document(),
+            options.passive()
+                ? WebFeature::kAddDocumentLevelPassiveTrueWheelEventListener
+                : WebFeature::kAddDocumentLevelPassiveFalseWheelEventListener);
+      } else {
+        UseCounter::Count(
+            executing_window->document(),
+            WebFeature::kAddDocumentLevelPassiveDefaultWheelEventListener);
       }
     }
   }

third_party/blink/renderer/core/dom/events/event_target.h

@@ -180,6 +180,9 @@ class CORE_EXPORT EventTarget : public ScriptWrappable {
 
   virtual bool KeepEventInNode(Event*) { return false; }
 
+  // Returns true if the target is window, window.document, or window.document.body.
+  bool IsTopLevelNode();
+
  protected:
   EventTarget();
 

third_party/blink/renderer/core/events/wheel_event.cc

@@ -24,6 +24,7 @@
 #include "third_party/blink/renderer/core/events/wheel_event.h"
 
 #include "third_party/blink/renderer/core/clipboard/data_transfer.h"
+#include "third_party/blink/renderer/core/frame/use_counter.h"
 
 namespace blink {
 
@@ -115,6 +116,19 @@ bool WheelEvent::IsWheelEvent() const {
   return true;
 }
 
+void WheelEvent::preventDefault() {
+  UIEventWithKeyState::preventDefault();
+
+  if (HandlingPassive() == PassiveMode::kNotPassiveDefault &&
+      currentTarget()->IsTopLevelNode()) {
+    if (ExecutionContext* context = currentTarget()->GetExecutionContext()) {
+      UseCounter::Count(
+          context,
+          WebFeature::kDocumentLevelPassiveDefaultEventListenerPreventedWheel);
+    }
+  }
+}
+
 DispatchEventResult WheelEvent::DispatchEvent(EventDispatcher& dispatcher) {
   return dispatcher.Dispatch();
 }

third_party/blink/renderer/core/events/wheel_event.h

@@ -70,6 +70,8 @@ class CORE_EXPORT WheelEvent final : public MouseEvent {
   bool IsMouseEvent() const override;
   bool IsWheelEvent() const override;
 
+  void preventDefault() override;
+
   const WebMouseWheelEvent& NativeEvent() const { return native_event_; }
 
   // WheelEvent doesn't modify the event path, but its parent MouseEvent does.

tools/metrics/histograms/enums.xml

@@ -19469,6 +19469,11 @@ Called by update_net_error_codes.py.-->
   <int value="2515" label="V8RTCRtpTransceiver_Direction_AttributeSetter"/>
   <int value="2516" label="HTMLLinkElementDisabledByParser"/>
   <int value="2517" label="RequestIsHistoryNavigation"/>
+  <int value="2518" label="AddDocumentLevelPassiveTrueWheelEventListener"/>
+  <int value="2519" label="AddDocumentLevelPassiveFalseWheelEventListener"/>
+  <int value="2520" label="AddDocumentLevelPassiveDefaultWheelEventListener"/>
+  <int value="2521"
+      label="DocumentLevelPassiveDefaultEventListenerPreventedWheel"/>
 </enum>
 
 <enum name="FeedbackSource">