Simplify platform_canvas.h by recognizing that PlatformCanvas does not actually extend

ui/gfx/canvas_paint_gtk.cc

 // 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.
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/canvas_skia_paint.h"
 #include "ui/gfx/rect.h"
 
@@ skipping 34 matching lines @@
     gdk_cairo_region(cr, region_);
     cairo_fill(cr);
     cairo_destroy(cr);
   }
 
   gdk_region_destroy(region_);
 }
 
 void CanvasSkiaPaint::Init(bool opaque) {
   GdkRectangle bounds = rectangle();
+  RecreateBackingCanvas(gfx::Size(bounds.width, bounds.height),
+                        ui::SCALE_FACTOR_100P, opaque);
+
   skia::PlatformCanvas* canvas = platform_canvas();
-  if (!canvas->initialize(bounds.width, bounds.height, opaque, NULL)) {
-    // Cause a deliberate crash;
-    CHECK(false);
-  }
-  // No need to clear the canvas, because cairo automatically performs the
-  // clear.
 
   // Need to translate so that the dirty region appears at the origin of the
   // surface.
   canvas->translate(-SkIntToScalar(bounds.x), -SkIntToScalar(bounds.y));
 
   context_ = skia::BeginPlatformPaint(canvas);
 }
 
 } // namespace gfx