Fix recording of kAnimatingScrollOnMain

ui/events/blink/input_handler_proxy.cc

Index: ui/events/blink/input_handler_proxy.cc
diff --git a/ui/events/blink/input_handler_proxy.cc b/ui/events/blink/input_handler_proxy.cc
index 377f6bddcbf73ce8b50cd054d5c9dc40524408dc..56917e5332045d9f66606d39979e9765f9c15047 100644
--- a/ui/events/blink/input_handler_proxy.cc
+++ b/ui/events/blink/input_handler_proxy.cc
@@ -427,6 +427,14 @@ void InputHandlerProxy::RecordMainThreadScrollingReasons(
        ++i) {
     unsigned val = 1 << i;
     if (reasons & val) {
+      if (val == cc::MainThreadScrollingReason::kAnimatingScrollOnMainThread) {
+        // We only want to record "animating scroll on main thread" reason if
+        // it's the only reason. If it's not the only reason, the "real" reason
+        // for scrolling on main is something else, and we only want to pay
+        // attention to that reason.
+        if (reasons & ~val)
+          continue;
+      }
       if (device == blink::WebGestureDeviceTouchscreen) {
         UMA_HISTOGRAM_ENUMERATION(
             kGestureHistogramName, i + 1,