Only scroll on main if the targeted frames need to scroll on main

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

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@kde.org)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights
    reserved.
 
    This library is free software; you can redistribute it and/or
@@ skipping 46 matching lines @@
 #include <memory>
 
 namespace blink {
 
 class AXObjectCache;
 class ComputedStyle;
 class DocumentLifecycle;
 class Cursor;
 class Element;
 class ElementVisibilityObserver;
+class Frame;
 class FloatSize;
 class JSONArray;
 class JSONObject;
 class LayoutItem;
 class LayoutViewItem;
 class LayoutPart;
 class LocalFrame;
 class KURL;
 class Node;
 class LayoutAnalyzer;
@@ skipping 683 matching lines @@
   void enqueueScrollAnchoringAdjustment(ScrollableArea*);
   void performScrollAnchoringAdjustments();
 
   // For PaintInvalidator temporarily. TODO(wangxianzhu): Move into
   // PaintInvalidator.
   void invalidatePaintIfNeeded(const PaintInvalidationState&);
 
   // Only for SPv2.
   std::unique_ptr<JSONObject> compositedLayersAsJSON(LayerTreeFlags);
 
+  // Recursively update frame tree. Each frame has its only

[pdr., 2016/12/17 05:50:16]

+1, nice comment.

[yigu, 2016/12/18 17:57:11]

Thanks for your previous suggestion on this :)

+  // scroll on main reason. Given the following frame tree
+  //   A
+  //  / \
+  // B   C
+  // |
+  // D
+  // If B has fixed background-attachment but other frames
+  // don't, both A and C should scroll on cc. Frame D should
+  // scrolled on main thread as its ancestor B.
+  void updateSubFrameScrollOnMainReason(const Frame&,
+                                        MainThreadScrollingReasons);
+  String mainThreadScrollingReasonsAsText() const;
+  MainThreadScrollingReasons mainThreadScrollingReasons() const;
+  MainThreadScrollingReasons mainThreadScrollingReasonsPerFrame(
+      const LocalFrame&) const;
+  bool hasVisibleSlowRepaintViewportConstrainedObjects(const FrameView&) const;
+
  protected:
   // Scroll the content via the compositor.
   bool scrollContentsFastPath(const IntSize& scrollDelta);
 
   // Scroll the content by invalidating everything.
   void scrollContentsSlowPath();
 
   ScrollBehavior scrollBehaviorStyle() const override;
 
   void scrollContentsIfNeeded();
@@ skipping 345 matching lines @@
   struct ObjectPaintInvalidation {
     String name;
     PaintInvalidationReason reason;
   };
   std::unique_ptr<Vector<ObjectPaintInvalidation>>
       m_trackedObjectPaintInvalidations;
 
   // For Slimming Paint v2 only.
   std::unique_ptr<PaintController> m_paintController;
   std::unique_ptr<PaintArtifactCompositor> m_paintArtifactCompositor;
+
+  MainThreadScrollingReasons m_lastMainThreadScrollingReasons;

[pdr., 2016/12/17 05:50:16]

Is "last" important? m_mainThreadScrollingReasons may be simpler.

[yigu, 2016/12/18 17:57:11]

Done.

 };
 
 inline void FrameView::incrementVisuallyNonEmptyCharacterCount(unsigned count) {
   if (m_isVisuallyNonEmpty)
     return;
   m_visuallyNonEmptyCharacterCount += count;
   // Use a threshold value to prevent very small amounts of visible content from
   // triggering didMeaningfulLayout.  The first few hundred characters rarely
   // contain the interesting content of the page.
   static const unsigned visualCharacterThreshold = 200;
@@ skipping 20 matching lines @@
                   widget.isFrameView());
 DEFINE_TYPE_CASTS(FrameView,
                   ScrollableArea,
                   scrollableArea,
                   scrollableArea->isFrameView(),
                   scrollableArea.isFrameView());
 
 }  // namespace blink
 
 #endif  // FrameView_h