Ensure that blending is disabled for layers with no alpha

ui/gfx/compositor/layer.cc

Index: ui/gfx/compositor/layer.cc
diff --git a/ui/gfx/compositor/layer.cc b/ui/gfx/compositor/layer.cc
index 53097bdc5c228da508048719005d77559facf15d..214b07e302018d8d1e316d1072e0af46ae625e2e 100644
--- a/ui/gfx/compositor/layer.cc
+++ b/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);