Plumb preferred raster scale for background images from Blink to cc layers.

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

 // Copyright 2014 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 BackgroundImageGeometry_h
 #define BackgroundImageGeometry_h
 
 #include "core/paint/PaintPhase.h"
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/geometry/LayoutRect.h"
@@ skipping 12 matching lines @@
 
  public:
   BackgroundImageGeometry() : m_hasNonLocalGeometry(false) {}
 
   void calculate(const LayoutBoxModelObject&,
                  const LayoutBoxModelObject* paintContainer,
                  const GlobalPaintFlags,
                  const FillLayer&,
                  const LayoutRect& paintRect);
 
+  // destRect() is the rect in the space of the containing box into which to
+  // draw the image. If the image is repeated via tiling, tileSize() is the size
+  // in pixels of the box to draw the image once.
+  //
+  // tileSize() need not be the same as the intrinsic size of the image; if not,
+  // it means the image will be resized (via an image filter) when painted into
+  // that tile region.
+  //
+  // spaceSize().width in the horizontal and spaceSize().height in the vertical
+  // direction are the spaces between tiles, if the image is tiled.
   const LayoutRect& destRect() const { return m_destRect; }
   const LayoutSize& tileSize() const { return m_tileSize; }
   const LayoutPoint& phase() const { return m_phase; }
   // Space-size represents extra width and height that may be added to
   // the image if used as a pattern with background-repeat: space.
   const LayoutSize& spaceSize() const { return m_repeatSpacing; }
   // Has background-attachment: fixed. Implies that we can't always cheaply
   // compute destRect.
   bool hasNonLocalGeometry() const { return m_hasNonLocalGeometry; }
 
@@ skipping 29 matching lines @@
   LayoutRect m_destRect;
   LayoutPoint m_phase;
   LayoutSize m_tileSize;
   LayoutSize m_repeatSpacing;
   bool m_hasNonLocalGeometry;
 };
 
 }  // namespace blink
 
 #endif  // BackgroundImageGeometry_h