Move WebMouseWheelEvent into its own header file.

ui/events/blink/input_handler_proxy.h

 // 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.
 
 #ifndef UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_H_
 #define UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_H_
 
 #include <memory>
 
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
 #include "cc/input/input_handler.h"
 #include "third_party/WebKit/public/platform/WebGestureCurve.h"
 #include "third_party/WebKit/public/platform/WebGestureCurveTarget.h"
 #include "third_party/WebKit/public/platform/WebGestureEvent.h"
 #include "third_party/WebKit/public/platform/WebInputEvent.h"
 #include "third_party/WebKit/public/web/WebActiveWheelFlingParameters.h"
 #include "ui/events/blink/blink_features.h"
 #include "ui/events/blink/input_scroll_elasticity_controller.h"
 #include "ui/events/blink/scoped_web_input_event.h"
 #include "ui/events/blink/synchronous_input_handler_proxy.h"
 
 namespace base {
 class TickClock;
 }
 
+namespace blink {
+class WebMouseWheelEvent;
+}
+
 namespace ui {
 
 namespace test {
 class InputHandlerProxyTest;
 class InputHandlerProxyEventQueueTest;
 }
 
 class CompositorThreadEventQueue;
 class EventWithCallback;
 class InputHandlerProxyClient;
@@ skipping 212 matching lines @@
   bool has_ongoing_compositor_scroll_pinch_;
 
   std::unique_ptr<base::TickClock> tick_clock_;
 
   DISALLOW_COPY_AND_ASSIGN(InputHandlerProxy);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_BLINK_INPUT_HANDLER_PROXY_H_