Add UMA metric for tracking listeners for blocking touch while fling is happening

content/renderer/input/input_handler_manager.cc

Index: content/renderer/input/input_handler_manager.cc
diff --git a/content/renderer/input/input_handler_manager.cc b/content/renderer/input/input_handler_manager.cc
index d4a6c9db94b82f65b87112db05931bca7f0f0bb6..b6deb4c0b187c2064f916160e10aa46aff04cebb 100644
--- a/content/renderer/input/input_handler_manager.cc
+++ b/content/renderer/input/input_handler_manager.cc
@@ -245,6 +245,10 @@ void InputHandlerManager::DidOverscroll(int routing_id,
   client_->DidOverscroll(routing_id, params);
 }
 
+void InputHandlerManager::DidStartFlinging(int routing_id) {
+  client_->DidStartFlinging(routing_id);
+}
+
 void InputHandlerManager::DidStopFlinging(int routing_id) {
   client_->DidStopFlinging(routing_id);
 }