Add LayerTreeHostClient::{will,did}UpdateLayer, report layer updates to DevTools

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index b3d004ac32b9840dd9cdbe182d6661e2e4f7a75f..23f2a454caf85cfa37bfc501c39980bfbc1cb9cc 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -260,6 +260,8 @@ class CC_EXPORT LayerTreeHost : NON_EXPORTED_BASE(public RateLimiterClient) {
       bool update_total_num_cc_layers_can_use_lcd_text,
       bool update_total_num_cc_layers_will_use_lcd_text);
 
+  int id() const { return tree_id_; }
+
  protected:
   LayerTreeHost(LayerTreeHostClient* client, const LayerTreeSettings& settings);
   bool Initialize(scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner);
@@ -365,6 +367,7 @@ class CC_EXPORT LayerTreeHost : NON_EXPORTED_BASE(public RateLimiterClient) {
     int64 total_num_cc_layers_will_use_lcd_text;
   };
   LCDTextMetrics lcd_text_metrics_;
+  int tree_id_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHost);
 };