Log to UMA why we would load a third-party frame

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 419d75ec172dbeecae388a6c79699fff76fb6e8e..35d4fbbbbf42bc5802b849f3a6507da5d2daf093 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -4308,11 +4308,28 @@ void FrameView::updateViewportIntersectionIfNeeded() {
   m_viewportIntersectionValid = true;
   FrameView* parent = parentFrameView();
   if (!parent) {
+    HTMLFrameOwnerElement* element = frame().deprecatedLocalOwner();
+    if (!element)
+      frame().document()->maybeRecordLoadReason(WouldLoadOutOfProcess);
+    // Having no layout object means the frame is not drawn.
+    else if (!element->layoutObject())
+      frame().document()->maybeRecordLoadReason(WouldLoadDisplayNone);
     m_viewportIntersection = frameRect();
     return;
   }
   ASSERT(!parent->m_needsUpdateViewportIntersection);
 
+  bool parentLoaded = parent->frame().document()->wouldLoadReason() > Created;
+  // If the parent wasn't loaded, the children won't be either.
+  if (parentLoaded) {
+    if (frameRect().isEmpty())
+      frame().document()->maybeRecordLoadReason(WouldLoadZeroByZero);
+    else if (frameRect().maxY() < 0)
+      frame().document()->maybeRecordLoadReason(WouldLoadAbove);
+    else if (frameRect().maxX() < 0)
+      frame().document()->maybeRecordLoadReason(WouldLoadLeft);
+  }
+
   // If our parent is hidden, then we are too.
   if (parent->m_viewportIntersection.isEmpty()) {
     m_viewportIntersection = parent->m_viewportIntersection;
@@ -4332,6 +4349,9 @@ void FrameView::updateViewportIntersectionIfNeeded() {
   // content while scrolling.
   IntRect viewport = parent->m_viewportIntersection;
   m_viewportIntersection.intersect(viewport);
+
+  if (parentLoaded && !m_viewportIntersection.isEmpty())
+    frame().document()->maybeRecordLoadReason(WouldLoadVisible);
 }
 
 void FrameView::updateViewportIntersectionsForSubtree(
@@ -4417,8 +4437,6 @@ void FrameView::notifyRenderThrottlingObservers() {
 
   updateThrottlingStatus();
 
-  frame().document()->onVisibilityMaybeChanged(!m_hiddenForThrottling);
-
   bool becameThrottled = !wasThrottled && canThrottleRendering();
   bool becameUnthrottled = wasThrottled && !canThrottleRendering();
   ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator();