[Aura] Support transparent webkit.

content/browser/renderer_host/backing_store_skia.cc

Index: content/browser/renderer_host/backing_store_skia.cc
diff --git a/content/browser/renderer_host/backing_store_skia.cc b/content/browser/renderer_host/backing_store_skia.cc
index 1c04363b70aabbdfd5592b99ac4850240a1d23a6..cc461061f4db4d6e753a46793b9f7d63a7bb38e8 100644
--- a/content/browser/renderer_host/backing_store_skia.cc
+++ b/content/browser/renderer_host/backing_store_skia.cc
@@ -24,6 +24,7 @@ BackingStoreSkia::BackingStoreSkia(RenderWidgetHost* widget,
   bitmap_.setConfig(SkBitmap::kARGB_8888_Config, size.width(), size.height());
   bitmap_.allocPixels();
   canvas_.reset(new SkCanvas(bitmap_));
+  copy_paint_.setXfermodeMode(SkXfermode::kSrc_Mode);
 }
 
 BackingStoreSkia::~BackingStoreSkia() {
@@ -73,7 +74,7 @@ void BackingStoreSkia::PaintToBackingStore(
     SkRect dstrect = SkRect::MakeXYWH(
         SkIntToScalar(copy_rect.x()), SkIntToScalar(copy_rect.y()),
         SkIntToScalar(w), SkIntToScalar(h));
-    canvas_.get()->drawBitmapRect(sk_bitmap, &srcrect, dstrect);
+    canvas_.get()->drawBitmapRect(sk_bitmap, &srcrect, dstrect, &copy_paint_);

[brettw, 2011/10/21 20:14:44]

In other places we haven't bothered saving the SkPaint. I'd probably just create
it on the stack when you need it, unless you have a strong reason to do it like
this.

[xiyuan, 2011/10/21 20:24:05]

Done.

   }
 }