Add UMA stats for pinch-zoom behavior on Android

third_party/WebKit/Source/web/WebViewImpl.cpp

Index: third_party/WebKit/Source/web/WebViewImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebViewImpl.cpp b/third_party/WebKit/Source/web/WebViewImpl.cpp
index a20c4c51ab3c0c1208d5c916a971d4eb0e729c4e..51b48b97066a306fe0cbb49fa3afa8aa12af1c6d 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -2072,6 +2072,8 @@ bool WebViewImpl::handleInputEvent(const WebInputEvent& inputEvent)
         autofillClient->firstUserGestureObserved();
     }
 
+    page()->frameHost().visualViewport().startTrackingPinchStats();

[Yoav Weiss, 2015/09/25 08:46:59]

Would that mean that we start tracking pinch zoom regardless of the input event
type?

[bokan, 2015/09/25 17:01:48]

Yes, I use it more as a signal that this is something the user can see and
interact with. Though on Android I think that's pretty much just touches...

+
     TRACE_EVENT1("input", "WebViewImpl::handleInputEvent", "type", inputTypeToName(inputEvent.type).ascii());
     // If we've started a drag and drop operation, ignore input events until
     // we're done.
@@ -4227,8 +4229,10 @@ void WebViewImpl::applyViewportDeltas(
     visualViewportOffset.move(visualViewportDelta.width, visualViewportDelta.height);
     setPageScaleFactorAndLocation(pageScaleFactor() * pageScaleDelta, visualViewportOffset);
 
-    if (pageScaleDelta != 1)
+    if (pageScaleDelta != 1) {

[Yoav Weiss, 2015/09/25 08:46:59]

What's the pageScaleDelta value in non-mobile zoom-out scenarios? I'd assume
it's lower than 1 and would be counted as a scale change.

[bokan, 2015/09/25 17:01:48]

This is the delta coming from the compositor. As such, it's only the *change* in
page scale that occured on the compositor that Blink doesn't know about yet. The
only changes from the compositor are due to pinch-zoom, double-tap to zoom
animations, and zoom-to-legible text editing. The initial page scale that gets
set on non-mobile pages is done from the Blink main thread and sent to the
compositor.

         m_doubleTapZoomPending = false;
+        page()->frameHost().visualViewport().userDidChangeScale();
+    }
 
     m_elasticOverscroll += elasticOverscrollDelta;
     frameView->didUpdateElasticOverscroll();