Optionally clear PlatformCanvas instances.

ui/gfx/native_theme_win.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 "ui/gfx/native_theme_win.h"
 
 #include <windows.h>
 #include <uxtheme.h>
 #include <vsstyle.h>
 #include <vssym32.h>
@@ skipping 412 matching lines @@
                                               State state,
                                               const gfx::Rect& rect,
                                               const ExtraParams& extra) const {
   // TODO(asvitkine): This path is pretty inefficient - for each paint operation
   //                  it creates a new offscreen bitmap Skia canvas. This can
   //                  be sped up by doing it only once per part/state and
   //                  keeping a cache of the resulting bitmaps.
 
   // Create an offscreen canvas that is backed by an HDC.
   scoped_ptr<SkCanvas> offscreen_canvas(
-      skia::CreateBitmapCanvas(rect.width(), rect.height(), false));
+      skia::CreateBitmapCanvas(rect.width(), rect.height(),
+                               skia::PlatformDevice::FLAGS_INITIALIZED));

[Jeff Timanus, 2012/02/23 22:14:10]

This file is windows specific, so the initialization can be explicitly
performed.

   DCHECK(offscreen_canvas.get());
   DCHECK(skia::SupportsPlatformPaint(offscreen_canvas.get()));
 
   // Some of the Windows theme drawing operations do not write correct alpha
   // values for fully-opaque pixels; instead the pixels get alpha 0. This is
   // especially a problem on Windows XP or when using the Classic theme.
   //
   // To work-around this, mark all pixels with a placeholder value, to detect
   // which pixels get touched by the paint operation. After paint, set any
   // pixels that have alpha 0 to opaque and placeholders to fully-transparent.
@@ skipping 1309 matching lines @@
     handle = open_theme_(NULL, L"Spin");
     break;
   default:
     NOTREACHED();
   }
   theme_handles_[theme_name] = handle;
   return handle;
 }
 
 }  // namespace gfx