Add more specific metrics for main thread scrolling reasons

third_party/WebKit/Source/core/frame/FrameView.h

Index: third_party/WebKit/Source/core/frame/FrameView.h
diff --git a/third_party/WebKit/Source/core/frame/FrameView.h b/third_party/WebKit/Source/core/frame/FrameView.h
index f3496595a49b91242f2929265d357eb26dab8317..d825a9a9ac4cc1486f418850df1c7e3749c64b61 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.h
+++ b/third_party/WebKit/Source/core/frame/FrameView.h
@@ -767,6 +767,21 @@ class CORE_EXPORT FrameView final
   // Only for SPv2.
   std::unique_ptr<JSONObject> compositedLayersAsJSON(LayerTreeFlags);
 
+  inline int reasonIndex(uint32_t reason) const {

[bokan, 2016/12/13 14:38:57]

inline unneeded, this is inline by virtue of being defined in the class
declaration.

[bokan, 2016/12/13 14:38:57]

This should move as a helper into MainThreadScrollingReason.h

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

Done.

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

Done.

+    if (!reason || reason & (reason - 1))
+      return 0;
+    int power = 0;
+    while (reason > 0) {
+      reason = reason >> 1;
+      ++power;
+    }
+    return power;
+  }
+
+  void adjustMainThreadReasonsDueToLayoutObject(uint32_t reason, bool increase);

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

IMO, this should be called adjustMainThreadReasons or
adjustMainThreadReasonsFromStyle

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

Done.

+
+  MainThreadScrollingReasons checkMainThreadScrollingReasonDueToLayoutObject();

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

check->get, Reason->Reasons

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

Done.

+
  protected:
   // Scroll the content via the compositor.
   bool scrollContentsFastPath(const IntSize& scrollDelta);
@@ -1132,6 +1147,12 @@ class CORE_EXPORT FrameView final
   // For Slimming Paint v2 only.
   std::unique_ptr<PaintController> m_paintController;
   std::unique_ptr<PaintArtifactCompositor> m_paintArtifactCompositor;
+
+  // For recording main thread scrolling reasons
+  // due to layout object properties. e.g. opacity, transform.
+  // The size of the vector depends on the number of
+  // main thread scrolling reasons.
+  Vector<int> m_mainThreadScrollingReasonLayoutCounter;

[bokan, 2016/12/13 14:38:57]

My read is that this vector is tracking scrolling reasons for all scrollers in a
FrameView (other than the FrameView itself) and they all get combined together
for a page-wide bitmask. In which case this doesn't belong here (we're trying to
remove scrolling from FrameView anyway, so it wouldn't belong here in any case).
Perhaps this should just be in ScrollingCoordinator itself, globally, for the
whole page.

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

Done.

 };
 
 inline void FrameView::incrementVisuallyNonEmptyCharacterCount(unsigned count) {