Optionally clear PlatformCanvas instances.

ui/gfx/canvas_skia.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/canvas_skia.h"
 
 #include <limits>
 
 #include "base/i18n/rtl.h"
 #include "base/logging.h"
@@ skipping 36 matching lines @@
 
 namespace gfx {
 
 ////////////////////////////////////////////////////////////////////////////////
 // CanvasSkia, public:
 
 CanvasSkia::CanvasSkia(const gfx::Size& size, bool is_opaque)
     : owned_canvas_(new skia::PlatformCanvas(size.width(), size.height(),
                                              is_opaque)),
       canvas_(owned_canvas_.get()) {
+#if defined(OS_WIN) || defined(OS_MACOSX)
+  // skia::PlatformCanvas instances are initialized to 0 by Cairo on Linux, but
+  // uninitialized on Win and Mac.
+  if (!is_opaque)
+    owned_canvas_->clear(SkColorSetARGB(0, 0, 0, 0));
+#endif
 }
 
 CanvasSkia::CanvasSkia(const SkBitmap& bitmap, bool is_opaque)
     : owned_canvas_(new skia::PlatformCanvas(bitmap.width(), bitmap.height(),
                                              is_opaque)),
       canvas_(owned_canvas_.get()) {
   DrawBitmapInt(bitmap, 0, 0);
 }
 
 CanvasSkia::CanvasSkia()
@@ skipping 307 matching lines @@
 // CanvasSkia, private:
 
 bool CanvasSkia::IntersectsClipRectInt(int x, int y, int w, int h) {
   SkRect clip;
   return canvas_->getClipBounds(&clip) &&
       clip.intersect(SkIntToScalar(x), SkIntToScalar(y), SkIntToScalar(x + w),
                      SkIntToScalar(y + h));
 }
 
 }  // namespace gfx