Allow CanvasSkia to bind to an existing SkCanvas.

ui/gfx/canvas_skia_mac.mm

 // Copyright (c) 2011 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.
 
 #import <Cocoa/Cocoa.h>
 
 #include "ui/gfx/canvas_skia.h"
 
 #include "base/mac/mac_util.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/sys_string_conversions.h"
 #include "third_party/skia/include/core/SkShader.h"
 #include "ui/gfx/font.h"
 #include "ui/gfx/rect.h"
 
 namespace gfx {
 
-CanvasSkia::CanvasSkia(int width, int height, bool is_opaque)
-    : skia::PlatformCanvas(width, height, is_opaque) {
-}
-
-CanvasSkia::CanvasSkia() : skia::PlatformCanvas() {
-}
-
-CanvasSkia::~CanvasSkia() {
-}
-
 // static
 void CanvasSkia::SizeStringInt(const string16& text,
                                const gfx::Font& font,
                                int* width, int* height,
                                int flags) {
   NSFont* native_font = font.GetNativeFont();
   NSString* ns_string = base::SysUTF16ToNSString(text);
   NSDictionary* attributes =
       [NSDictionary dictionaryWithObject:native_font
                                   forKey:NSFontAttributeName];
   NSSize string_size = [ns_string sizeWithAttributes:attributes];
   *width = string_size.width;
   *height = font.GetHeight();
 }
 
 void CanvasSkia::DrawStringInt(const string16& text,
                                const gfx::Font& font,
                                const SkColor& color,
                                int x, int y, int w, int h,
                                int flags) {
   if (!IntersectsClipRectInt(x, y, w, h))
     return;
 
-  skia::ScopedPlatformPaint scoped_platform_paint(this);
+  skia::ScopedPlatformPaint scoped_platform_paint(canvas_);
   CGContextRef context = scoped_platform_paint.GetPlatformSurface();
   CGContextSaveGState(context);
 
   NSColor* ns_color = [NSColor colorWithDeviceRed:SkColorGetR(color) / 255.0
                                             green:SkColorGetG(color) / 255.0
                                              blue:SkColorGetB(color) / 255.0
                                             alpha:SkColorGetA(color) / 255.0];
   NSMutableParagraphStyle *ns_style =
       [[[NSMutableParagraphStyle alloc] init] autorelease];
   if (flags & TEXT_ALIGN_CENTER)
@@ skipping 23 matching lines @@
   CTFrameDraw(frame, context);
   CGContextRestoreGState(context);
 }
 
 ui::TextureID CanvasSkia::GetTextureID() {
   // TODO(wjmaclean)
   return 0;
 }
 
 }  // namespace gfx