Add a Canvas::SaveAndUnscale() method for pixel-accurate drawing.

ui/gfx/canvas.h

 // Copyright (c) 2012 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 UI_GFX_CANVAS_H_
 #define UI_GFX_CANVAS_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 151 matching lines @@
   // Extracts an ImageSkiaRep from the contents of this canvas.
   ImageSkiaRep ExtractImageRep() const;
 
   // Draws a dashed rectangle of the specified color.
   void DrawDashedRect(const Rect& rect, SkColor color);
 
   // Saves a copy of the drawing state onto a stack, operating on this copy
   // until a balanced call to Restore() is made.
   void Save();
 
+  // Saves the drawing state, unscales by the image scale factor, and returns
+  // that factor.  This is useful when callers want to draw directly in the
+  // native scale.
+  float SaveAndUnscale();
+
   // As with Save(), except draws to a layer that is blended with the canvas
   // at the specified alpha once Restore() is called.
   // |layer_bounds| are the bounds of the layer relative to the current
   // transform.
   void SaveLayerAlpha(uint8 alpha);
   void SaveLayerAlpha(uint8 alpha, const Rect& layer_bounds);
 
   // Restores the drawing state after a call to Save*(). It is an error to
   // call Restore() more times than Save*().
   void Restore();
@@ skipping 258 matching lines @@
 
   skia::RefPtr<skia::PlatformCanvas> owned_canvas_;
   SkCanvas* canvas_;
 
   DISALLOW_COPY_AND_ASSIGN(Canvas);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_CANVAS_H_