Merge 125445 - [chromium] Clear HUD canvas contents before drawing into it.

Source/WebCore/platform/graphics/chromium/cc/CCHeadsUpDisplayLayerImpl.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 54 matching lines @@
         m_hudTexture = CCScopedTexture::create(resourceProvider);
 
     // FIXME: Scale the HUD by deviceScale to make it more friendly under high DPI.
 
     if (m_hudTexture->size() != bounds())
         m_hudTexture->free();
 
     if (!m_hudTexture->id() && !m_hudTexture->allocate(CCRenderer::ImplPool, bounds(), GraphicsContext3D::RGBA, CCResourceProvider::TextureUsageAny))
         return;
 
-    // Render pixels into the texture.
-    OwnPtr<SkCanvas> canvas = adoptPtr(skia::CreateBitmapCanvas(bounds().width(), bounds().height(), false /* opaque */));
-    drawHudContents(canvas.get());
+    SkISize canvasSize;
+    if (m_hudCanvas)
+        canvasSize = m_hudCanvas->getDeviceSize();
+    else
+        canvasSize.set(0, 0);
 
-    const SkBitmap* bitmap = &canvas->getDevice()->accessBitmap(false);
+    if (canvasSize.fWidth != bounds().width() || canvasSize.fHeight != bounds().height() || !m_hudCanvas)
+        m_hudCanvas = adoptPtr(skia::CreateBitmapCanvas(bounds().width(), bounds().height(), false /* opaque */));
+
+    m_hudCanvas->clear(SkColorSetARGB(0, 0, 0, 0));
+    drawHudContents(m_hudCanvas.get());
+
+    const SkBitmap* bitmap = &m_hudCanvas->getDevice()->accessBitmap(false);
     SkAutoLockPixels locker(*bitmap);
 
     IntRect layerRect(IntPoint(), bounds());
     ASSERT(bitmap->config() == SkBitmap::kARGB_8888_Config);
     resourceProvider->upload(m_hudTexture->id(), static_cast<const uint8_t*>(bitmap->getPixels()), layerRect, layerRect, layerRect);
 }
 
 void CCHeadsUpDisplayLayerImpl::appendQuads(CCQuadSink& quadList, const CCSharedQuadState* sharedQuadState, bool&)
 {
     if (!m_hudTexture->id())
@@ skipping 174 matching lines @@
         canvas->drawRect(skRect, paint);
 
         paint.setColor(strokeColor);
         paint.setStyle(SkPaint::kStroke_Style);
         paint.setStrokeWidth(2);
         canvas->drawRect(skRect, paint);
     }
 }
 
 }