Add flag for drawing layers to screen with Ganesh

cc/layers/layer_impl.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/layers/layer_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "base/stringprintf.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/scrollbar_animation_controller.h"
@@ skipping 542 matching lines @@
   NoteLayerPropertyChanged();
   NoteLayerPropertyChangedForDescendants();
 }
 
 void LayerImpl::NoteLayerPropertyChangedForDescendants() {
   layer_tree_impl()->set_needs_update_draw_properties();
   for (size_t i = 0; i < children_.size(); ++i)
     children_[i]->NoteLayerPropertyChangedForSubtree();
 }
 
+bool LayerImpl::CanDrawDirectlyToBackbuffer() const {

[danakj, 2013/05/15 20:33:16]

I don't like bringing a "composite draw property" into the layer level really.

Could this be a value on draw properties that is computed by LTHCommon?

Or alternatively, a function on DrawProperties? It would then instead need a
state on DrawProps to know that it draws to the root target.

And while we're here, why did you choose to limit this to the root surface only?

[enne (OOO), 2013/05/15 22:34:38]

Moved to DrawProperties.  PTAL.
Limiting to non-1 opacity is because you need to composite all the draw calls in
the picture together before drawing that layer.  This is the picture analogy to
needing to create a render surface for non-1 opacity.

As for the root layer, there'd been some discussion about an initial use for
Ganesh in places where we could get LCD text where we otherwise wouldn't, such
as when you're drawing a layer directly to the backbuffer and not into a render
target.  I just figured we could start there.

What do you think?

+  return render_target() == layer_tree_impl_->root_layer() &&
+      draw_opacity() == 1.f && !draw_opacity_is_animating();
+}
+
 const char* LayerImpl::LayerTypeAsString() const {
   return "Layer";
 }
 
 void LayerImpl::ResetAllChangeTrackingForSubtree() {
   layer_property_changed_ = false;
   layer_surface_property_changed_ = false;
 
   update_rect_ = gfx::RectF();
 
@@ skipping 454 matching lines @@
     state->Set("replica_layer", replica_layer_->AsValue().release());
 }
 
 scoped_ptr<base::Value> LayerImpl::AsValue() const {
   scoped_ptr<base::DictionaryValue> state(new base::DictionaryValue());
   AsValueInto(state.get());
   return state.PassAs<base::Value>();
 }
 
 }  // namespace cc