Add flag for drawing layers to screen with Ganesh

cc/trees/layer_tree_host_common.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_common.h"
 
 #include <algorithm>
 
 #include "base/debug/trace_event.h"
 #include "cc/base/math_util.h"
@@ skipping 1249 matching lines @@
     // The surface's cached clip rect value propagates regardless of what
     // clipping goes on between layers here.
     clip_rect_for_subtree_in_descendant_space =
         clip_rect_from_ancestor_in_descendant_space;
 
     // Layers that are not their own render_target will render into the target
     // of their nearest ancestor.
     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;
 
   gfx::Rect rect_in_target_space = ToEnclosingRect(
       MathUtil::MapClippedRect(layer->draw_transform(), content_rect));
 
   if (LayerClipsSubtree(layer)) {
     subtree_should_be_clipped = true;
     if (ancestor_clips_subtree && !layer->render_surface()) {
       clip_rect_for_subtree = clip_rect_from_ancestor;
@@ skipping 526 matching lines @@
   // At this point, we think the point does hit the touch event handler region
   // on the layer, but we need to walk up the parents to ensure that the layer
   // was not clipped in such a way that the hit point actually should not hit
   // the layer.
   if (PointIsClippedBySurfaceOrClipRect(screen_space_point, layer_impl))
     return false;
 
   return true;
 }
 }  // namespace cc