Move WebMouseWheelEvent into its own header file.

ui/events/blink/input_scroll_elasticity_controller_unittest.cc

 // Copyright 2014 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_scroll_elasticity_controller.h"
 
 #include "cc/input/input_handler.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/WebKit/public/platform/WebInputEvent.h"
+#include "third_party/WebKit/public/platform/WebMouseWheelEvent.h"
 
 namespace ui {
 namespace {
 
 enum Phase {
   PhaseNone = blink::WebMouseWheelEvent::PhaseNone,
   PhaseBegan = blink::WebMouseWheelEvent::PhaseBegan,
   PhaseStationary = blink::WebMouseWheelEvent::PhaseStationary,
   PhaseChanged = blink::WebMouseWheelEvent::PhaseChanged,
   PhaseEnded = blink::WebMouseWheelEvent::PhaseEnded,
@@ skipping 395 matching lines @@
     TickCurrentTimeAndAnimate();
     if (helper_.StretchAmount().IsZero())
       break;
     ticks_to_zero += 1;
   }
   EXPECT_GT(ticks_to_zero, 3);
 }
 
 }  // namespace
 }  // namespace ui