Add CompositingReasons to compositor layers.

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 0390f049e56efb8c20bda4dcf18407b64dfda8ae..be8d71ef63af208274f4812653d69c405d3fb835 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -40,6 +40,7 @@ Layer::Layer()
       have_wheel_event_handlers_(false),
       anchor_point_(0.5f, 0.5f),
       background_color_(0),
+      compositing_reasons_(kCompositingReasonUnknown),
       opacity_(1.f),
       anchor_point_z_(0.f),
       is_container_for_fixed_position_layers_(false),
@@ -643,6 +644,7 @@ void Layer::PushPropertiesTo(LayerImpl* layer) {
   layer->SetContentBounds(content_bounds());
   layer->SetContentsScale(contents_scale_x(), contents_scale_y());
   layer->SetDebugName(debug_name_);
+  layer->SetCompositingReasons(compositing_reasons_);
   layer->SetDoubleSided(double_sided_);
   layer->SetDrawCheckerboardForMissingTiles(
       draw_checkerboard_for_missing_tiles_);
@@ -749,6 +751,12 @@ void Layer::SetDebugName(const std::string& debug_name) {
   SetNeedsCommit();
 }
 
+void Layer::SetCompositingReasons(CompositingReasons reasons) {
+  // For now this is only debug information, so we avoid calling
+  // SetNeedsCommit() which causes invalidations in some code paths.

[jamesr, 2013/05/28 23:20:05]

Do you expect this to become something other than debug information in the
future?

+  compositing_reasons_ = reasons;
+}
+
 void Layer::CreateRenderSurface() {
   DCHECK(!draw_properties_.render_surface);
   draw_properties_.render_surface = make_scoped_ptr(new RenderSurface(this));