Add latency measurement system

cc/layer_tree_host_client.h

Index: cc/layer_tree_host_client.h
diff --git a/cc/layer_tree_host_client.h b/cc/layer_tree_host_client.h
index 6657f59a8f268e8e7e4004810d31d3a327f28e41..37eb742e0e8b0cd3a3e277ea0b0513b2398de1e2 100644
--- a/cc/layer_tree_host_client.h
+++ b/cc/layer_tree_host_client.h
@@ -11,6 +11,10 @@ namespace gfx {
 class Vector2d;
 }
 
+namespace WebKit {
+struct WebLatencyInfoImpl;
+}
+
 namespace cc {
 class FontAtlas;
 class InputHandler;
@@ -31,6 +35,7 @@ public:
     virtual void didCommit() = 0;
     virtual void didCommitAndDrawFrame() = 0;
     virtual void didCompleteSwapBuffers() = 0;
+    virtual void onReceivedLatencyInfo(const WebKit::WebLatencyInfoImpl&) = 0;
 
     // Used only in the single-threaded path.
     virtual void scheduleComposite() = 0;