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

content/renderer/android/synchronous_compositor_filter.cc

Index: content/renderer/android/synchronous_compositor_filter.cc
diff --git a/content/renderer/android/synchronous_compositor_filter.cc b/content/renderer/android/synchronous_compositor_filter.cc
index d81b40787f19fa9bb4a4b93da2fca0660f66953f..9bde7f386e0f74d44ea472a0279c9cbc7f57e1e0 100644
--- a/content/renderer/android/synchronous_compositor_filter.cc
+++ b/content/renderer/android/synchronous_compositor_filter.cc
@@ -241,6 +241,8 @@ void SynchronousCompositorFilter::DidOverscroll(
   proxy->DidOverscroll(params);
 }
 
+void SynchronousCompositorFilter::DidStartFlinging(int routing_id) {}
+
 void SynchronousCompositorFilter::DidStopFlinging(int routing_id) {
   DCHECK(compositor_task_runner_->BelongsToCurrentThread());
   Send(new InputHostMsg_DidStopFlinging(routing_id));