Add more specific metrics for main thread scrolling reasons

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@gmail.com>
@@ skipping 89 matching lines @@
       m_needsCompositedScrolling(false),
       m_rebuildHorizontalScrollbarLayer(false),
       m_rebuildVerticalScrollbarLayer(false),
       m_needsScrollOffsetClamp(false),
       m_needsRelayout(false),
       m_hadHorizontalScrollbarBeforeRelayout(false),
       m_hadVerticalScrollbarBeforeRelayout(false),
       m_scrollbarManager(*this),
       m_scrollCorner(nullptr),
       m_resizer(nullptr),
-      m_scrollAnchor(this)
+      m_scrollAnchor(this),
+      m_reasons(0)
 #if DCHECK_IS_ON()
       ,
       m_hasBeenDisposed(false)
 #endif
 {
   Node* node = box().node();
   if (node && node->isElementNode()) {
     // We save and restore only the scrollOffset as the other scroll values are
     // recalculated.
     Element* element = toElement(node);
@@ skipping 19 matching lines @@
 
   if (LocalFrame* frame = box().frame()) {
     if (FrameView* frameView = frame->view()) {
       frameView->removeScrollableArea(this);
       frameView->removeAnimatingScrollableArea(this);
     }
   }
 
   if (box().frame() && box().frame()->page()) {
     if (ScrollingCoordinator* scrollingCoordinator =
-            box().frame()->page()->scrollingCoordinator())
+            box().frame()->page()->scrollingCoordinator()) {
+      // Decrese the number of layer that has any main thread
+      // scrolling reasons stored in ScrollingCoordinator
+      for (uint32_t i = 0;
+           i < MainThreadScrollingReason::kMainThreadScrollingReasonCount;
+           ++i) {
+        if (hasMainThreadScrollingReason(1 << i)) {
+          scrollingCoordinator->adjustMainThreadReasonsFromStyle(1 << i, false);
+        }
+      }
       scrollingCoordinator->willDestroyScrollableArea(this);

[bokan, 2016/12/14 13:28:59]

Actually, since we already have this willDestroyScrollableArea in
ScrollingCoordinator, it makes more sense for the above code to go in there
since its specific to ScrollingCoordinator.

[yigu, 2016/12/14 21:17:33]

Done.

+    }
   }
 
   if (!box().documentBeingDestroyed()) {
     Node* node = box().node();
     // FIXME: Make setSavedLayerScrollOffset take DoubleSize. crbug.com/414283.
     if (node && node->isElementNode())
       toElement(node)->setSavedLayerScrollOffset(m_scrollOffset);
   }
 
   if (LocalFrame* frame = box().frame()) {
@@ skipping 1871 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollOffsetClampScope::
     clampScrollableAreas() {
   for (auto& scrollableArea : *s_needsClamp)
     scrollableArea->clampScrollOffsetAfterOverflowChange();
   delete s_needsClamp;
   s_needsClamp = nullptr;
 }
 
 }  // namespace blink