Record non-stacking-context as main thread scrolling reasons

third_party/WebKit/Source/core/paint/PaintLayer.h

Index: third_party/WebKit/Source/core/paint/PaintLayer.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.h b/third_party/WebKit/Source/core/paint/PaintLayer.h
index 83691b8b2a5b1467e59f4bee882dd28c06d63e57..4af963f60f95ae75716c887b0b75ba38dcc1af72 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -588,7 +588,8 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
 
   // Returns true if background phase is painted opaque in the given rect.
   // The query rect is given in local coordinates.
-  bool BackgroundIsKnownToBeOpaqueInRect(const LayoutRect&) const;
+  bool BackgroundIsKnownToBeOpaqueInRect(const LayoutRect&,
+                                         uint32_t* reasons = nullptr) const;

[bokan, 2017/04/25 18:04:15]

Document this parameter in the comments. A more descriptive name would also be
helpful.

[yigu, 2017/04/26 15:38:36]

Done.

 
   bool ContainsDirtyOverlayScrollbars() const {
     return contains_dirty_overlay_scrollbars_;