Add support for flattening in GeometryMapper.

third_party/WebKit/Source/platform/graphics/paint/GeometryMapper.h

 // Copyright 2016 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 GeometryMapper_h
 #define GeometryMapper_h
 
 #include "platform/graphics/paint/FloatClipRect.h"
 #include "platform/graphics/paint/PropertyTreeState.h"
 #include "platform/transforms/TransformationMatrix.h"
@@ skipping 95 matching lines @@
   //
   // |mappingRect| is both input and output.
   void ancestorToLocalRect(
       const TransformPaintPropertyNode* ancestorTransformNode,
       const TransformPaintPropertyNode* localTransformNode,
       FloatRect& mappingRect);
 
   // Returns the matrix used in |LocalToAncestorRect|. DCHECK fails iff
   // |localTransformNode| is not equal to or a descendant of
   // |ancestorTransformNode|.
+  // This matrix may not be flattened. Since GeometryMapper only supports
+  // flattened ancestor spaces, the returned matrix must be flattened to have
+  // the correct semantics (calling mapRect() on it implicitly applies
+  // flattening to the input; flattenTo2d() does it explicitly to tme matrix).
   const TransformationMatrix& localToAncestorMatrix(
       const TransformPaintPropertyNode* localTransformNode,
       const TransformPaintPropertyNode* ancestorTransformNode);
 
   // Returns the "clip visual rect" between |localTransformState| and
   // |ancestorState|. See above for the definition of "clip visual rect".
   FloatClipRect localToAncestorClipRect(
       const PropertyTreeState& localTransformState,
       const PropertyTreeState& ancestorState);
 
@@ skipping 67 matching lines @@
   const TransformationMatrix m_identity;
   const FloatClipRect m_infiniteClip;
   FloatClipRect m_tempRect;
 
   DISALLOW_COPY_AND_ASSIGN(GeometryMapper);
 };
 
 }  // namespace blink
 
 #endif  // GeometryMapper_h