Move the message definitions to their own files.

xfa/fwl/core/cfwl_msgmouse.h

Index: xfa/fwl/core/cfwl_msgmouse.h
diff --git a/xfa/fwl/core/cfwl_msgmouse.h b/xfa/fwl/core/cfwl_msgmouse.h
new file mode 100644
index 0000000000000000000000000000000000000000..c617ac1d4242b5380794dddffeb7c1bceb6aa26e
--- /dev/null
+++ b/xfa/fwl/core/cfwl_msgmouse.h
@@ -0,0 +1,40 @@
+// Copyright 2016 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
+
+#ifndef XFA_FWL_CORE_CFWL_MSGMOUSE_H_
+#define XFA_FWL_CORE_CFWL_MSGMOUSE_H_
+
+#include "xfa/fwl/core/cfwl_message.h"
+
+enum class FWL_MouseCommand {
+  LeftButtonDown,
+  LeftButtonUp,
+  LeftButtonDblClk,
+  RightButtonDown,
+  RightButtonUp,
+  RightButtonDblClk,
+  Move,
+  Enter,
+  Leave,
+  Hover
+};
+
+class CFWL_MsgMouse : public CFWL_Message {
+ public:
+  CFWL_MsgMouse();
+  ~CFWL_MsgMouse() override;
+
+  // CFWL_Message
+  std::unique_ptr<CFWL_Message> Clone() override;
+  CFWL_MessageType GetClassID() const override;
+
+  FX_FLOAT m_fx;
+  FX_FLOAT m_fy;
+  uint32_t m_dwFlags;
+  FWL_MouseCommand m_dwCmd;
+};
+
+#endif  // XFA_FWL_CORE_CFWL_MSGMOUSE_H_