Make UMA_HISTOGRAM_ENUMERATION work with scoped enums.

ui/events/blink/input_handler_proxy.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/events/blink/input_handler_proxy.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 
@@ skipping 538 matching lines @@
 
   if (device != blink::WebGestureDeviceTouchpad &&
       device != blink::WebGestureDeviceTouchscreen) {
     return;
   }
 
   // UMA_HISTOGRAM_ENUMERATION requires that the enum_max must be strictly
   // greater than the sample value. kMainThreadScrollingReasonCount doesn't
   // include the NotScrollingOnMain enum but the histograms do so adding
   // the +1 is necessary.
-  uint32_t mainThreadScrollingReasonEnumMax =
+  // TODO(dcheng): Fix https://crbug.com/705169 so this isn't needed.
+  constexpr uint32_t mainThreadScrollingReasonEnumMax =
       cc::MainThreadScrollingReason::kMainThreadScrollingReasonCount + 1;
   if (reasons == cc::MainThreadScrollingReason::kNotScrollingOnMain) {
     if (device == blink::WebGestureDeviceTouchscreen) {
       UMA_HISTOGRAM_ENUMERATION(
           kGestureHistogramName,
           cc::MainThreadScrollingReason::kNotScrollingOnMain,
           mainThreadScrollingReasonEnumMax);
     } else {
       UMA_HISTOGRAM_ENUMERATION(
           kWheelHistogramName,
@@ skipping 1046 matching lines @@
                  scroll_elasticity_controller_->GetWeakPtr(), gesture_event,
                  scroll_result));
 }
 
 void InputHandlerProxy::SetTickClockForTesting(
     std::unique_ptr<base::TickClock> tick_clock) {
   tick_clock_ = std::move(tick_clock);
 }
 
 }  // namespace ui