[Debugging] Make debug string more clear at GestureTapDown

Right now at TouchActionFilter::FilterGestureEvent, if there is a
GestureTapDown, we append an "O" into the debug string. This CL makes
it append "O1" if the |scrolling_touch_action_| has value, and "O2"
if it doesn't.

TBR=dtapuska@chromium.org

Bug: None
Change-Id: I71cd23cef21e73add2bb5c3f5ec9af0ca7acb4e6
Reviewed-on: https://chromium-review.googlesource.com/1195812Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587324}

content/browser/renderer_host/input/touch_action_filter.cc

@@ -174,13 +174,16 @@ FilterGestureEventResult TouchActionFilter::FilterGestureEvent(
       break;
 
     case WebInputEvent::kGestureTapDown:
-      gesture_sequence_.append("O");
       gesture_sequence_in_progress_ = true;
       // If the gesture is hitting a region that has a non-blocking (such as a
       // passive) event listener.
       if (gesture_event->is_source_touch_event_set_non_blocking)
         SetTouchAction(cc::kTouchActionAuto);
       scrolling_touch_action_ = allowed_touch_action_;
+      if (scrolling_touch_action_.has_value())
+        gesture_sequence_.append("O1");
+      else
+        gesture_sequence_.append("O2");
       DCHECK(!drop_current_tap_ending_event_);
       break;