Invalidate objects when containing block changed

third_party/WebKit/Source/core/layout/LayoutObject.h

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index c6697f74031bf3c15fb8e506454cf652bc2cda6f..313dce1f69032d3ea3975a7032affc3c46a10b89 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -770,6 +770,7 @@ public:
     // the layoutObject returned is an ancestor of |paintInvalidationContainer|.
     LayoutObject* container(const LayoutBoxModelObject* paintInvalidationContainer = nullptr, bool* paintInvalidationContainerSkipped = nullptr) const;
     LayoutObject* containerCrossingFrameBoundaries() const;
+    // Finds the container as if this object is a fixed position element.

[chrishtr, 2015/10/30 18:28:18]

Is it ever called for an object which is not fixed position?

[Xianzhu, 2015/10/30 19:15:28]

Now LayoutBlock::styleWillChange() calls this to find the current containing
block of its fixed-position descendants. The block may become a containing
block, so it needs to find the original containing block of the descendants and
change their containing block relationships.

Now the method works in the similar way as containingBlockForAbsolutePosition()
which also doesn't require the caller is absolute-position.

     LayoutBlock* containerForFixedPosition(const LayoutBoxModelObject* paintInvalidationContainer = nullptr, bool* paintInvalidationContainerSkipped = nullptr) const;
     LayoutBlock* containingBlockForAbsolutePosition() const;
 
@@ -1504,7 +1505,7 @@ private:
 
     inline void invalidateContainerPreferredLogicalWidths();
 
-    void invalidatePaintOfPreviousPaintInvalidationRect(const LayoutBoxModelObject& paintInvalidationContainer, PaintInvalidationReason) const;
+    void invalidatePaintOfPreviousPaintInvalidationRect(const LayoutBoxModelObject& paintInvalidationContainer, PaintInvalidationReason);
 
     LayoutRect previousSelectionRectForPaintInvalidation() const;
     void setPreviousSelectionRectForPaintInvalidation(const LayoutRect&);