Update paint property subtrees on paint offset changes

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PaintPropertyTreeBuilder_h
 #define PaintPropertyTreeBuilder_h
 
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
@@ skipping 78 matching lines @@
 // animation, mask, filter, ... etc.
 // It expects to be invoked for each layout tree node in DOM order during
 // InPrePaint phase.
 class PaintPropertyTreeBuilder {
  public:
   PaintPropertyTreeBuilderContext setupInitialContext();
   // Update the paint properties for a frame and ensure the context is up to
   // date.
   void updateProperties(FrameView&, PaintPropertyTreeBuilderContext&);
 
-  // Update the context to account for positioning. This can affect the
-  // current paint offset, for example, but no paint properties are updated.
+  // Update the context to account for positioning. No paint properties are
+  // updated but this can affect the current paint offset which will force a
+  // subtree update.
   void updateContextForBoxPosition(const LayoutObject&,
                                    PaintPropertyTreeBuilderContext&);
 
   // Update the paint properties that affect this object (e.g., properties like
   // paint offset translation) and ensure the context is up to date.
   void updatePropertiesForSelf(const LayoutObject&,
                                PaintPropertyTreeBuilderContext&);
   // Update the paint properties that affect children of this object (e.g.,
   // scroll offset transform) and ensure the context is up to date.
   void updatePropertiesForChildren(const LayoutObject&,
@@ skipping 24 matching lines @@
   static void updateScrollAndScrollTranslation(
       const LayoutObject&,
       PaintPropertyTreeBuilderContext&);
   static void updateOutOfFlowContext(const LayoutObject&,
                                      PaintPropertyTreeBuilderContext&);
 };
 
 }  // namespace blink
 
 #endif  // PaintPropertyTreeBuilder_h