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 28f16070705b806c73c9fb0d64247bae852ef067..94e06e68dc45bdbaacdc05989c0df58f2a321f12 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -4270,11 +4270,14 @@ void FrameView::notifyRenderThrottlingObservers()
 {
     TRACE_EVENT0("blink", "FrameView::notifyRenderThrottlingObservers");
     DCHECK(!isInPerformLayout());
-    DCHECK(!m_frame->document() || !m_frame->document()->inStyleRecalc());
+    DCHECK(frame().document());
+    DCHECK(!frame().document()->inStyleRecalc());
     bool wasThrottled = canThrottleRendering();
 
     updateThrottlingStatus();
 
+    frame().document()->onVisibilityMaybeChanged(!m_hiddenForThrottling);
+
     bool becameThrottled = !wasThrottled && canThrottleRendering();
     bool becameUnthrottled = wasThrottled && !canThrottleRendering();
     ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator();