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

chrome/renderer/safe_browsing/phishing_thumbnailer.cc

Index: chrome/renderer/safe_browsing/phishing_thumbnailer.cc
===================================================================
--- chrome/renderer/safe_browsing/phishing_thumbnailer.cc	(revision 167659)
+++ chrome/renderer/safe_browsing/phishing_thumbnailer.cc	(working copy)
@@ -32,10 +32,12 @@
   }
   WebView* view = render_view->GetWebView();
   base::TimeTicks beginning_time = base::TimeTicks::Now();
-  skia::PlatformCanvas canvas;
-  if (!canvas.initialize(view_size.width(), view_size.height(), true)) {
+  SkCanvas* canvas = skia::CreatePlatformCanvas(view_size.width(),
+                                                view_size.height(), true, 0,
+                                                skia::RETURN_NULL_ON_FAILURE);
+  if (!canvas)
     return SkBitmap();
-  }
+  SkAutoUnref au(canvas);
 
   // Make sure we are not using any zoom when we take the snapshot.  We will
   // restore the previous zoom level after the snapshot is taken.
@@ -49,10 +51,10 @@
   view->mainFrame()->setCanHaveScrollbars(false);  // always hide scrollbars.
   view->resize(view_size);
   view->layout();
-  view->paint(webkit_glue::ToWebCanvas(&canvas),
+  view->paint(webkit_glue::ToWebCanvas(canvas),
               WebRect(0, 0, view_size.width(), view_size.height()));
 
-  SkDevice* device = skia::GetTopDevice(canvas);
+  SkDevice* device = skia::GetTopDevice(*canvas);
 
   // Now resize the thumbnail to the right size.  Note: it is important that we
   // use this resize algorithm here.