Add more specific metrics for main thread scrolling reasons

third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp

Index: third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
diff --git a/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp b/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
index 126c7e1df78494e91d952b882db88a6f2079a263..7fb7316bceffcc11fd734ff53df9f5cc4b32a5cd 100644
--- a/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -95,7 +95,10 @@ ScrollingCoordinator::ScrollingCoordinator(Page* page)
       m_touchEventTargetRectsAreDirty(false),
       m_shouldScrollOnMainThreadDirty(false),
       m_wasFrameScrollable(false),
-      m_lastMainThreadScrollingReasons(0) {}
+      m_lastMainThreadScrollingReasons(0),
+      m_mainThreadScrollingReasonsCounter(
+          MainThreadScrollingReason::kMainThreadScrollingReasonCount,
+          0) {}
 
 ScrollingCoordinator::~ScrollingCoordinator() {
   DCHECK(!m_page);
@@ -290,6 +293,7 @@ void ScrollingCoordinator::updateLayerPositionConstraint(PaintLayer* layer) {
 
 void ScrollingCoordinator::willDestroyScrollableArea(
     ScrollableArea* scrollableArea) {
+  removeStyleRelatedMainThreadScrollingReasonsForLayer(scrollableArea);
   removeWebScrollbarLayer(scrollableArea, HorizontalScrollbar);
   removeWebScrollbarLayer(scrollableArea, VerticalScrollbar);
 }
@@ -1169,6 +1173,9 @@ MainThreadScrollingReasons ScrollingCoordinator::mainThreadScrollingReasons()
     if (frameView->hasBackgroundAttachmentFixedObjects())
       reasons |=
           MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects;
+
+    reasons |= getStyleRelatedMainThreadScrollingReasons();
+
     FrameView::ScrollingReasons scrollingReasons =
         frameView->getScrollingReasons();
     const bool mayBeScrolledByInput =
@@ -1222,4 +1229,44 @@ bool ScrollingCoordinator::frameViewIsDirty() const {
   return false;
 }
 
+void ScrollingCoordinator::removeStyleRelatedMainThreadScrollingReasonsForLayer(
+    ScrollableArea* scrollableArea) {
+  // Decrese the number of layer that has any main thread

[bokan, 2016/12/19 21:25:14]

nit: layer->layers, has->have

[yigu, 2016/12/20 01:41:19]

Done.

+  // scrolling reasons stored in ScrollingCoordinator
+  if (scrollableArea->isPaintLayerScrollableArea()) {
+    PaintLayerScrollableArea* paintLayerScrollableArea =
+        toPaintLayerScrollableArea(scrollableArea);
+    for (uint32_t i = 0;
+         i < MainThreadScrollingReason::kMainThreadScrollingReasonCount; ++i) {
+      if (paintLayerScrollableArea->hasMainThreadScrollingReason(1 << i)) {

[bokan, 2016/12/19 21:25:14]

Nit: might be clearer to store and reuse 1 << i

[yigu, 2016/12/20 01:41:19]

Done.

+        paintLayerScrollableArea->flipMainThreadScrollingReason(1 << i);

[bokan, 2016/12/19 21:25:14]

You have adding a reason go through PLSA and call into ScrollingCoordinator but
removing go through ScrollingCoordinator and adjust the PLSA. They should work
the same way. IMO, this method should be on PLSA and decrement the
ScrollingCoordinator counts from there.

[yigu, 2016/12/20 01:41:19]

Done.

+        adjustStyleRelatedMainThreadScrollingReasons(1 << i, false);
+      }
+    }
+  }
+}
+
+void ScrollingCoordinator::adjustStyleRelatedMainThreadScrollingReasons(
+    const uint32_t reason,
+    bool increase) {
+  int index = MainThreadScrollingReason::getReasonIndex(reason);
+  DCHECK_GE(index, 0);
+  m_mainThreadScrollingReasonsCounter[index] += increase ? 1 : -1;
+  DCHECK_GE(m_mainThreadScrollingReasonsCounter[index], 0);
+}
+
+MainThreadScrollingReasons
+ScrollingCoordinator::getStyleRelatedMainThreadScrollingReasons() const {
+  MainThreadScrollingReasons reasons =
+      static_cast<MainThreadScrollingReasons>(0);
+  for (uint32_t reason = 1;
+       reason < MainThreadScrollingReason::kMainThreadScrollingReasonCount;
+       ++reason) {
+    if (m_mainThreadScrollingReasonsCounter[reason] > 0) {
+      reasons |= 1 << (reason - 1);
+    }
+  }
+  return reasons;
+}
+
 }  // namespace blink