Ensure that blending is disabled for layers with no alpha

BUG=5110667
TEST=None

Review URL: http://codereview.chromium.org/7597001
Patch from Ian Vollick <vollick@chromium.org>.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@95834 0039d316-1c4b-4281-b951-d872f2087c98

ui/gfx/compositor/layer.cc

@@ -89,8 +89,9 @@ void Layer::Draw() {
         static_cast<float>(layer->bounds_.y()));
   }
 
-  // Only blend for child layers. The root layer will clobber the cleared bg.
-  texture_draw_params.blend = parent_ != NULL;
+  // Only blend for transparent child layers.
+  // The root layer will clobber the cleared bg.
+  texture_draw_params.blend = parent_ != NULL && !fills_bounds_opaquely_;
 
 #if defined(OS_WIN)
   texture_->Draw(texture_draw_params);