Move WebMouseEvent into its own header file.

third_party/WebKit/public/platform/WebMouseWheelEvent.h

 // 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.
 
 #ifndef WebMouseWheelEvent_h
 #define WebMouseWheelEvent_h
 
-#include "WebInputEvent.h"
+#include "WebMouseEvent.h"
 
 namespace blink {
 
 // See WebInputEvent.h for details why this pack is here.
 #pragma pack(push, 4)
 
 // WebMouseWheelEvent ---------------------------------------------------------
 
 class WebMouseWheelEvent : public WebMouseEvent {
  public:
@@ skipping 76 matching lines @@
   BLINK_PLATFORM_EXPORT WebMouseWheelEvent flattenTransform() const;
 
   bool isCancelable() const { return dispatchType == Blocking; }
 #endif
 };
 #pragma pack(pop)
 
 }  // namespace blink
 
 #endif  // WebMouseWheelEvent_h