Add Vector2d classes that represent offsets, instead of using Point.

content/common/drag_messages.h

 // Copyright (c) 2012 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.
 
 // IPC messages for drag and drop.
 // Multiply-included message file, hence no include guard.
 
 #include "content/public/common/common_param_traits.h"
 #include "ipc/ipc_message_macros.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebDragOperation.h"
 #include "ui/gfx/point.h"
+#include "ui/gfx/vector2d.h"
 #include "webkit/glue/webdropdata.h"
 
 #define IPC_MESSAGE_START DragMsgStart
 
 // Messages sent from the browser to the renderer.
 
 IPC_MESSAGE_ROUTED5(DragMsg_TargetDragEnter,
                     WebDropData /* drop_data */,
                     gfx::Point /* client_pt */,
                     gfx::Point /* screen_pt */,
@@ skipping 27 matching lines @@
 // Messages sent from the renderer to the browser.
 
 // Used to tell the parent the user started dragging in the content area. The
 // WebDropData struct contains contextual information about the pieces of the
 // page the user dragged. The parent uses this notification to initiate a
 // drag session at the OS level.
 IPC_MESSAGE_ROUTED4(DragHostMsg_StartDragging,
                     WebDropData /* drop_data */,
                     WebKit::WebDragOperationsMask /* ops_allowed */,
                     SkBitmap /* image */,
-                    gfx::Point /* image_offset */)
+                    gfx::Vector2d /* image_offset */)
 
 // The page wants to update the mouse cursor during a drag & drop operation.
 // |is_drop_target| is true if the mouse is over a valid drop target.
 IPC_MESSAGE_ROUTED1(DragHostMsg_UpdateDragCursor,
                     WebKit::WebDragOperation /* drag_operation */)
 
 // Notifies the host that the renderer finished a drop operation.
 IPC_MESSAGE_ROUTED0(DragHostMsg_TargetDrop_ACK)