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

webkit/tools/test_shell/webwidget_host_gtk.cc

 // 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.
 
 #include "webkit/tools/test_shell/webwidget_host.h"
 
 #include <cairo/cairo.h>
 #include <gtk/gtk.h>
 
 #include "base/basictypes.h"
@@ skipping 339 matching lines @@
 
 void WebWidgetHost::Paint() {
   int width = logical_size_.width();
   int height = logical_size_.height();
   gfx::Rect client_rect(width, height);
 
   // Allocate a canvas if necessary
   if (!canvas_.get()) {
     ResetScrollRect();
     paint_rect_ = client_rect;
-    canvas_.reset(new skia::PlatformCanvas(width, height, true));
+    canvas_.reset(skia::CreatePlatformCanvas(width, height, true, 0,
+                                             skia::RETURN_NULL_ON_FAILURE));
     if (!canvas_.get()) {
       // memory allocation failed, we can't paint.
       LOG(ERROR) << "Failed to allocate memory for " << width << "x" << height;
       return;
     }
   }
 
   webwidget_->animate(0.0);
 
   // This may result in more invalidation
@@ skipping 55 matching lines @@
 
 void WebWidgetHost::PaintRect(const gfx::Rect& rect) {
   set_painting(true);
   webwidget_->paint(canvas_.get(), rect);
   set_painting(false);
 }
 
 void WebWidgetHost::WindowDestroyed() {
   delete this;
 }