Make first TouchStart and first TouchMove events on a flinging layer non-blocking

content/renderer/input/render_widget_input_handler.cc

Index: content/renderer/input/render_widget_input_handler.cc
diff --git a/content/renderer/input/render_widget_input_handler.cc b/content/renderer/input/render_widget_input_handler.cc
index ebc894b4d2068aba2f37ca5fd5b85251c2a96468..b1fdadc9c2aa0a437712fb40d412b15b1520200f 100644
--- a/content/renderer/input/render_widget_input_handler.cc
+++ b/content/renderer/input/render_widget_input_handler.cc
@@ -127,14 +127,14 @@ void LogPassiveEventListenersUma(WebInputEventResult result,
     PASSIVE_LISTENER_UMA_ENUM_SUPPRESSED,
     PASSIVE_LISTENER_UMA_ENUM_CANCELABLE,
     PASSIVE_LISTENER_UMA_ENUM_CANCELABLE_AND_CANCELED,
-    PASSIVE_LISTENER_UMA_ENUM_FORCED_NON_BLOCKING,
+    PASSIVE_LISTENER_UMA_ENUM_FORCED_NON_BLOCKING_DUE_TO_FLING,
     PASSIVE_LISTENER_UMA_ENUM_COUNT
   };
 
   int enum_value;
   switch (dispatch_type) {
-    case WebInputEvent::ListenersForcedNonBlockingPassive:
-      enum_value = PASSIVE_LISTENER_UMA_ENUM_FORCED_NON_BLOCKING;
+    case WebInputEvent::ListenersForcedNonBlockingPassiveDueToFling:
+      enum_value = PASSIVE_LISTENER_UMA_ENUM_FORCED_NON_BLOCKING_DUE_TO_FLING;
       break;
     case WebInputEvent::ListenersNonBlockingPassive:
       enum_value = PASSIVE_LISTENER_UMA_ENUM_PASSIVE;
@@ -164,10 +164,11 @@ void LogPassiveEventListenersUma(WebInputEventResult result,
       UMA_HISTOGRAM_CUSTOM_COUNTS("Event.PassiveListeners.Latency",
                                   GetEventLatencyMicros(event_timestamp, now),
                                   1, 10000000, 100);
-    } else if (enum_value == PASSIVE_LISTENER_UMA_ENUM_FORCED_NON_BLOCKING) {
+    } else if (enum_value ==
+               PASSIVE_LISTENER_UMA_ENUM_FORCED_NON_BLOCKING_DUE_TO_FLING) {
       base::TimeTicks now = base::TimeTicks::Now();
       UMA_HISTOGRAM_CUSTOM_COUNTS(
-          "Event.PassiveListeners.ForcedNonBlockingLatency",
+          "Event.PassiveListeners.ForcedNonBlockingLatencyDueToFling",
           GetEventLatencyMicros(event_timestamp, now), 1, 10000000, 100);
     }
   }
@@ -185,7 +186,8 @@ RenderWidgetInputHandler::RenderWidgetInputHandler(
       handling_event_type_(WebInputEvent::Undefined),
       context_menu_source_type_(ui::MENU_SOURCE_MOUSE),
       suppress_next_char_events_(false),
-      ignore_ack_for_mouse_move_from_debugger_(false) {
+      ignore_ack_for_mouse_move_from_debugger_(false),
+      waiting_for_first_touch_move_(false) {
   DCHECK(delegate);
   DCHECK(widget);
   delegate->SetInputHandler(this);
@@ -334,18 +336,22 @@ void RenderWidgetInputHandler::HandleInputEvent(
     LogPassiveEventListenersUma(processed, touch.dispatchType,
                                 input_event.timeStampSeconds, latency_info);
 
-    if (input_event.type == WebInputEvent::TouchStart &&
-        touch.dispatchType == WebInputEvent::Blocking &&
+    // TODO(lanwei): May remove it when we no longer need any metric for event
+    // latency outside fling.
+    if (touch.dispatchType == WebInputEvent::Blocking &&
         base::TimeTicks::IsHighResolution()) {
-      base::TimeTicks now = base::TimeTicks::Now();
-      if (touch.dispatchedDuringFling) {
-        UMA_HISTOGRAM_CUSTOM_COUNTS(
-            "Event.Touch.TouchStartLatencyDuringFling",
-            GetEventLatencyMicros(input_event.timeStampSeconds, now), 1,
-            100000000, 50);
-      } else {
+      bool touch_start_or_first_touch_move = false;
+      if (touch.type == WebInputEvent::TouchStart) {
+        waiting_for_first_touch_move_ = true;
+        touch_start_or_first_touch_move = true;
+      } else if (touch.type == WebInputEvent::TouchMove) {
+        touch_start_or_first_touch_move = waiting_for_first_touch_move_;
+        waiting_for_first_touch_move_ = false;
+      }
+      if (touch_start_or_first_touch_move) {
+        base::TimeTicks now = base::TimeTicks::Now();
         UMA_HISTOGRAM_CUSTOM_COUNTS(
-            "Event.Touch.TouchStartLatencyOutsideFling",
+            "Event.Touch.TouchLatencyOutsideFling",
             GetEventLatencyMicros(input_event.timeStampSeconds, now), 1,
             100000000, 50);
       }