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..f2ffdd6c330cfdf885d8b65dcddd65103c157a4e 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -1267,6 +1267,11 @@ static void CalculateDrawPropertiesInternal(
     layer_draw_properties.render_target = layer->parent()->render_target();
   }
 
+  layer_draw_properties.can_draw_directly_to_backbuffer =

[danakj, 2013/05/16 15:17:55]

Can you leave a comment explaining the checks done here?

[enne (OOO), 2013/05/16 20:34:11]

Done.

+      IsRootLayer(layer_draw_properties.render_target) &&
+      layer->draw_properties().opacity == 1.f &&
+      !animating_opacity_to_screen;

[danakj, 2013/05/16 15:17:55]

Why this? We'll generate a new frame with a new opacity and we can set it false
in that quad.

[enne (OOO), 2013/05/16 20:34:11]

Sure, but then for animation of opacity=1 to opacity=x, on frame 1 we won't have
the texture ready for future frames where we can't draw to the backbuffer and
will jank/checkerboard.  This is just an optimization.

+
   if (adjust_text_aa)
     layer_draw_properties.can_use_lcd_text = layer_can_use_lcd_text;