Add more specific metrics for main thread scrolling reasons

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 196f562691e386f9bdd7377e29038afb9aec1869..8469e696d032ed84dda81edac05a648dec563098 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -194,7 +194,10 @@ FrameView::FrameView(LocalFrame& frame)
       m_scrollbarManager(*this),
       m_needsScrollbarsUpdate(false),
       m_suppressAdjustViewSize(false),
-      m_allowsLayoutInvalidationAfterLayoutClean(true) {
+      m_allowsLayoutInvalidationAfterLayoutClean(true),
+      m_mainThreadScrollingReasonLayoutCounter(
+          MainThreadScrollingReason::kMainThreadScrollingReasonCount,
+          0) {
   init();
 }
 
@@ -4675,4 +4678,24 @@ int FrameView::initialViewportHeight() const {
   return m_initialViewportSize.height();
 }
 
+void FrameView::adjustMainThreadReasonsDueToLayoutObject(uint32_t reason,
+                                                         bool increase) {
+  m_mainThreadScrollingReasonLayoutCounter[reasonIndex(reason)] +=

[bokan, 2016/12/13 14:38:56]

This should never be negative, right? If so, please DCHECK that it isn't.

[yigu, 2016/12/13 20:54:10]

Done.

+      increase ? 1 : -1;
+}
+
+MainThreadScrollingReasons
+FrameView::checkMainThreadScrollingReasonDueToLayoutObject() {
+  MainThreadScrollingReasons reasons =
+      static_cast<MainThreadScrollingReasons>(0);
+  for (uint32_t reason = 1;
+       reason < MainThreadScrollingReason::kMainThreadScrollingReasonCount;
+       ++reason) {
+    if (m_mainThreadScrollingReasonLayoutCounter[reason] > 0) {
+      reasons |= 1 << (reason - 1);
+    }
+  }
+  return reasons;
+}
+
 }  // namespace blink