Add UMA metric for tracking root level listeners for blocking touch.

third_party/WebKit/Source/core/events/TouchEvent.cpp

Index: third_party/WebKit/Source/core/events/TouchEvent.cpp
diff --git a/third_party/WebKit/Source/core/events/TouchEvent.cpp b/third_party/WebKit/Source/core/events/TouchEvent.cpp
index 085c275c4bc8ed59f5f39a3945d3dc9e80d90be9..d8b89c9fcf55d8b3bb47d117d41105f6c375887c 100644
--- a/third_party/WebKit/Source/core/events/TouchEvent.cpp
+++ b/third_party/WebKit/Source/core/events/TouchEvent.cpp
@@ -28,13 +28,53 @@
 
 #include "bindings/core/v8/DOMWrapperWorld.h"
 #include "bindings/core/v8/ScriptState.h"
+#include "core/EventTypeNames.h"
 #include "core/events/EventDispatcher.h"
 #include "core/frame/FrameConsole.h"
+#include "core/frame/FrameView.h"
 #include "core/frame/LocalDOMWindow.h"
+#include "core/html/HTMLElement.h"

[tdresser, 2016/04/07 12:22:07]

Is this used?

[dtapuska, 2016/04/19 17:54:46]

Done.

 #include "core/inspector/ConsoleMessage.h"
+#include "platform/Histogram.h"
 
 namespace blink {
 
+namespace {
+
+const size_t kRootScrollerOffset = 4;

[tdresser, 2016/04/07 12:22:07]

Add a comment indicating what these are offsets into, why we need them etc.

[dtapuska, 2016/04/19 17:54:46]

Done.

+const size_t kScrollableDocumentOffset = 2;
+const size_t kHandledOffset = 1;
+
+enum ListenerHistogram {
+    NonRootScrollerNonScrollableNotHandled, // Non-root-scroller, non-scrollable document, not handled.
+    NonRootScrollerNonScrollableHandled, // Non-root-scroller, non-scrollable document, handled application.
+    NonRootScrollerScrollableDocumentNotHandled, // Non-root-scroller, scrollable document, not handled.
+    NonRootScrollerScrollableDocumentHandled, // Non-root-scroller, scrollable document, handled application.
+    RootScrollerNonScrollableNotHandled, // Root-scroller, non-scrollable document, not handled.
+    RootScrollerNonScrollableHandled, // Root-scroller, non-scrollable document, handled.
+    RootScrollerScrollableDocumentNotHandled, // Root-scroller, scrollable document, not handled.
+    RootScrollerScrollableDocumentHandled, // Root-scroller, scrollable document, handled.
+    ListenerHistogramMax,
+};
+
+ListenerHistogram toListenerHistogramValue(const Node& node, DispatchEventResult dispatchResult)
+{
+    int result = 0;
+    if (node.isDocumentNode() || static_cast<Node*>(node.document().documentElement()) == &node || static_cast<Node*>(node.document().body()) == &node) {

[tdresser, 2016/04/07 12:22:08]

We need to check |window| too, don't we?

Add a comment on what targets we're checking, and why.

[dtapuska, 2016/04/19 17:54:47]

Done.

+        result += kRootScrollerOffset;
+    }
+    FrameView* view = node.document().view();
+    if (view && view->isScrollable())
+        result += kScrollableDocumentOffset;
+
+    if (dispatchResult != DispatchEventResult::NotCanceled) {

[tdresser, 2016/04/07 12:22:07]

Let's be consistent about whether or not we use {} for if statements with single
line bodies.

[dtapuska, 2016/04/19 17:54:46]

Done.

+        result += kHandledOffset;
+    }
+    return (ListenerHistogram)result;

[tdresser, 2016/04/07 12:22:08]

static_cast

[dtapuska, 2016/04/19 17:54:47]

Done.

+}
+
+} // namespace
+
 TouchEvent::TouchEvent()
 {
 }
@@ -42,11 +82,15 @@ TouchEvent::TouchEvent()
 TouchEvent::TouchEvent(TouchList* touches, TouchList* targetTouches,
     TouchList* changedTouches, const AtomicString& type,
     AbstractView* view,
-    PlatformEvent::Modifiers modifiers, bool cancelable, bool causesScrollingIfUncanceled,
+    PlatformEvent::Modifiers modifiers, bool cancelable, bool causesScrollingIfUncanceled, bool firstTouchMoveAfterTouchStart,
     double platformTimeStamp)
     // Pass a sourceCapabilities including the ability to fire touchevents when creating this touchevent, which is always created from input device capabilities from EventHandler.
-    : UIEventWithKeyState(type, true, cancelable, view, 0, modifiers, platformTimeStamp, InputDeviceCapabilities::firesTouchEventsSourceCapabilities()),
-    m_touches(touches), m_targetTouches(targetTouches), m_changedTouches(changedTouches), m_causesScrollingIfUncanceled(causesScrollingIfUncanceled)
+    : UIEventWithKeyState(type, true, cancelable, view, 0, modifiers, platformTimeStamp, InputDeviceCapabilities::firesTouchEventsSourceCapabilities())
+    , m_touches(touches)
+    , m_targetTouches(targetTouches)
+    , m_changedTouches(changedTouches)
+    , m_causesScrollingIfUncanceled(causesScrollingIfUncanceled)
+    , m_firstTouchMoveAfterTouchStart(firstTouchMoveAfterTouchStart)
 {
 }
 
@@ -139,8 +183,17 @@ TouchEvent& TouchEventDispatchMediator::event() const
 
 DispatchEventResult TouchEventDispatchMediator::dispatchEvent(EventDispatcher& dispatcher) const
 {
-    event().eventPath().adjustForTouchEvent(event());
-    return dispatcher.dispatch();
+    TouchEvent& touchEvent = event();
+    touchEvent.eventPath().adjustForTouchEvent(touchEvent);
+    DispatchEventResult result = dispatcher.dispatch();
+
+    // Only report for top level documents with a single touch on
+    // touch-start or the first touch-move.
+    if (touchEvent.cancelable() && touchEvent.touches() && touchEvent.touches()->length() == 1 && !dispatcher.node().document().ownerElement() && (touchEvent.type() == EventTypeNames::touchstart || (touchEvent.type() == EventTypeNames::touchmove && touchEvent.firstTouchMoveAfterTouchStart()))) {

[tdresser, 2016/04/07 12:22:08]

This condition is pretty illegible. Maybe split this up into a few intermediate
booleans?

Or use a series of if's with early returns if the condition fails?

[dtapuska, 2016/04/19 17:54:47]

Done.

+        DEFINE_STATIC_LOCAL(EnumerationHistogram, rootDocumentListenerHistogram, ("Event.Listeners.TouchBlockingOnRootElements", ListenerHistogramMax));
+        rootDocumentListenerHistogram.count(toListenerHistogramValue(dispatcher.node(), result));
+    }
+    return result;
 }
 
 } // namespace blink