Log to UMA when x-origin frames (1) are created and (2) become visible

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index 50137729160c42130d6a2ec3d239691f308eca76..8a24f5d6bfe004126297e979cafae373622e3b32 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -4260,6 +4260,9 @@ void FrameView::notifyRenderThrottlingObservers()
 
     updateThrottlingStatus();
 
+    if (frame().document())

[dcheng, 2016/08/29 20:37:19]

Do we need to do this check because Widget isn't synchronously detached (see
UpdateSuspendScope)?

[dgrogan, 2016/08/31 19:52:41]

Not sure... I was cargo-culting from the first clause of line 4258's DCHECK that
implies frame().document() can be null.

[dcheng, 2016/09/01 21:24:26]

Looking at the code, I'm actually not sure how we'd end up in this situation. I
believe this task is only ever posted when we are attached (e.g. frame() is not
null) and the task itself is cancelled when the FrameView is disposed.

Can you try just asserting that frame().document() is non-null and see what
happens?

+        frame().document()->onVisibilityMaybeChanged(!m_hiddenForThrottling);
+
     bool becameThrottled = !wasThrottled && canThrottleRendering();
     bool becameUnthrottled = wasThrottled && !canThrottleRendering();
     ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator();