Allow CanvasSkia to bind to an existing SkCanvas.

skia/ext/canvas_paint_gtk.h

Index: skia/ext/canvas_paint_gtk.h
diff --git a/skia/ext/canvas_paint_gtk.h b/skia/ext/canvas_paint_gtk.h
index fca12cadcbde22d64ede03ca7351e7435bdce0ee..ade49af533f04dc9360a1c5dda463c64dd381063 100644
--- a/skia/ext/canvas_paint_gtk.h
+++ b/skia/ext/canvas_paint_gtk.h
@@ -8,6 +8,7 @@
 #pragma once
 
 #include "base/logging.h"
+#include "skia/ext/canvas_paint_common.h"
 #include "skia/ext/platform_canvas.h"
 
 #include <gdk/gdk.h>
@@ -39,7 +40,7 @@ class CanvasPaintT : public T {
 
   virtual ~CanvasPaintT() {
     if (!is_empty()) {
-      T::restoreToCount(1);
+      GetPlatformCanvas(this)->restoreToCount(1);
 
       // Blit the dirty rect to the window.
       CHECK(window_);
@@ -83,16 +84,17 @@ class CanvasPaintT : public T {
  private:
   void init(bool opaque) {
     GdkRectangle bounds = rectangle();
-    if (!T::initialize(bounds.width, bounds.height, opaque, NULL)) {
+    PlatformCanvas* canvas = GetPlatformCanvas(this);
+    if (!canvas->initialize(bounds.width, bounds.height, opaque, NULL)) {
       // Cause a deliberate crash;
       CHECK(false);
     }
 
     // Need to translate so that the dirty region appears at the origin of the
     // surface.
-    T::translate(-SkIntToScalar(bounds.x), -SkIntToScalar(bounds.y));
+    canvas->translate(-SkIntToScalar(bounds.x), -SkIntToScalar(bounds.y));
 
-    context_ = BeginPlatformPaint(this);
+    context_ = BeginPlatformPaint(canvas);
   }
 
   cairo_t* context_;