Add flag for drawing layers to screen with Ganesh

cc/trees/layer_tree_host_common.cc

Index: cc/trees/layer_tree_host_common.cc
diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index f0e5b8ff23ad897b03d2907367361aa8cfaa2b42..b8ab367d60755965c57d02ea1d75181810c5b816 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -1267,6 +1267,21 @@ static void CalculateDrawPropertiesInternal(
     layer_draw_properties.render_target = layer->parent()->render_target();
   }
 
+  // Mark whether a layer could be drawn directly to the back buffer, for
+  // example when it could use LCD text even though it's in a non-contents
+  // opaque layer.  This means that it can't be drawn to an intermediate
+  // render target and also that no blending is applied to the layer as a whole
+  // (meaning that its contents don't have to be pre-composited into a bitmap or
+  // a render target).
+  //
+  // Ignoring animations is an optimization,
+  // as it means that we're going to need some retained resources for this
+  // layer in the near future even if its opacity is 1 now.
+  layer_draw_properties.can_draw_directly_to_backbuffer =
+      IsRootLayer(layer_draw_properties.render_target) &&
+      layer->draw_properties().opacity == 1.f &&
+      !animating_opacity_to_screen;
+
   if (adjust_text_aa)
     layer_draw_properties.can_use_lcd_text = layer_can_use_lcd_text;