Add touch drag UMA latency metric.

content/browser/renderer_host/input/input_router_impl_perftest.cc

Index: content/browser/renderer_host/input/input_router_impl_perftest.cc
diff --git a/content/browser/renderer_host/input/input_router_impl_perftest.cc b/content/browser/renderer_host/input/input_router_impl_perftest.cc
index 9e24a51c53b45253f345a78582bd1c0b1e56dfc3..c0400b4585ee9fe91b708bfff2bfc7afa01cf602 100644
--- a/content/browser/renderer_host/input/input_router_impl_perftest.cc
+++ b/content/browser/renderer_host/input/input_router_impl_perftest.cc
@@ -81,6 +81,11 @@ class NullInputRouterClient : public InputRouterClient {
       const ui::LatencyInfo& latency_info) override {
     return INPUT_EVENT_ACK_STATE_NOT_CONSUMED;
   }
+  void OnForwardEventToRenderer(
+      const blink::WebInputEvent& event,
+      ui::LatencyInfo* latency) override {
+  }
+
   void IncrementInFlightEventCount() override {}
   void DecrementInFlightEventCount() override {}
   void OnHasTouchEventHandlers(bool has_handlers) override {}