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 fe04c5a66b7f62cd407af5223674f1da69f07753..e63b952b989ff24a13da3abf2683854e408293a0 100644
--- a/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -94,7 +94,10 @@ ScrollingCoordinator::ScrollingCoordinator(Page* page)
       m_touchEventTargetRectsAreDirty(false),
       m_shouldScrollOnMainThreadDirty(false),
       m_wasFrameScrollable(false),
-      m_lastMainThreadScrollingReasons(0) {}
+      m_lastMainThreadScrollingReasons(0),
+      m_mainThreadScrollingReasonLayoutCounter(
+          MainThreadScrollingReason::kMainThreadScrollingReasonCount,
+          0) {}
 
 ScrollingCoordinator::~ScrollingCoordinator() {
   DCHECK(!m_page);
@@ -1174,6 +1177,9 @@ MainThreadScrollingReasons ScrollingCoordinator::mainThreadScrollingReasons()
     if (frameView->hasBackgroundAttachmentFixedObjects())
       reasons |=
           MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects;
+
+    reasons |= getMainThreadScrollingReasonsFromStyle();
+
     FrameView::ScrollingReasons scrollingReasons =
         frameView->getScrollingReasons();
     const bool mayBeScrolledByInput =
@@ -1227,4 +1233,26 @@ bool ScrollingCoordinator::frameViewIsDirty() const {
   return false;
 }
 
+void ScrollingCoordinator::adjustMainThreadReasonsFromStyle(uint32_t reason,
+                                                            bool increase) {
+  int index = MainThreadScrollingReason::getReasonIndex(reason);
+  DCHECK_GE(index, 0);
+  DCHECK_GE(m_mainThreadScrollingReasonLayoutCounter[index], 0);

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

This check should be below the following line.

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

Done.

+  m_mainThreadScrollingReasonLayoutCounter[index] += increase ? 1 : -1;
+}
+
+MainThreadScrollingReasons
+ScrollingCoordinator::getMainThreadScrollingReasonsFromStyle() const {
+  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