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

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index 90ff24cc32f1ac7ab9010b59b016e97f9c341e8f..61c77f9999308aa70241e911d422be696fd99efb 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -354,6 +354,10 @@ void RenderWidgetCompositor::SetLatencyInfo(
   layer_tree_host_->SetLatencyInfo(latency_info);
 }
 
+int RenderWidgetCompositor::GetLayerTreeId() const {
+  return layer_tree_host_->id();
+}
+
 bool RenderWidgetCompositor::initialize(cc::LayerTreeSettings settings) {
   scoped_refptr<base::MessageLoopProxy> compositor_message_loop_proxy =
       RenderThreadImpl::current()->compositor_message_loop_proxy();