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 7d8bec7a9c89d7193d5f1fed653ba6a10cfb2829..9c6382f785c36fb270ecf87e2e928c92a3ec87d8 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -253,6 +253,7 @@ class CC_EXPORT LayerTreeHost : NON_EXPORTED_BASE(public RateLimiterClient) {
   bool in_paint_layer_contents() const { return in_paint_layer_contents_; }
 
   bool UsingSharedMemoryResources();
+  int id() const { return tree_id_; }
 
  protected:
   LayerTreeHost(LayerTreeHostClient* client, const LayerTreeSettings& settings);
@@ -364,6 +365,7 @@ 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);
 };