Move WebMouseWheelEvent into its own header file.

ui/events/blink/web_input_event_traits.cc

 // Copyright 2016 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/web_input_event_traits.h"
 
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
+#include "third_party/WebKit/public/platform/WebGestureEvent.h"
+#include "third_party/WebKit/public/platform/WebMouseWheelEvent.h"
 
 using base::StringAppendF;
 using base::SStringPrintf;
 using blink::WebGestureEvent;
 using blink::WebInputEvent;
 using blink::WebKeyboardEvent;
 using blink::WebMouseEvent;
 using blink::WebMouseWheelEvent;
 using blink::WebTouchEvent;
 using blink::WebTouchPoint;
@@ skipping 228 matching lines @@
 uint32_t WebInputEventTraits::GetUniqueTouchEventId(
     const WebInputEvent& event) {
   if (WebInputEvent::isTouchEventType(event.type)) {
     return static_cast<const WebTouchEvent&>(event).uniqueTouchEventId;
   }
   return 0U;
 }
 
 // static
 LatencyInfo WebInputEventTraits::CreateLatencyInfoForWebGestureEvent(
-    WebGestureEvent event) {
+    const WebGestureEvent& event) {
   SourceEventType source_event_type = SourceEventType::UNKNOWN;
   if (event.sourceDevice == blink::WebGestureDevice::WebGestureDeviceTouchpad) {
     source_event_type = SourceEventType::WHEEL;
   } else if (event.sourceDevice ==
              blink::WebGestureDevice::WebGestureDeviceTouchscreen) {
     source_event_type = SourceEventType::TOUCH;
   }
   LatencyInfo latency_info(source_event_type);
   return latency_info;
 }
 
 }  // namespace ui