Add support for touch based zoom gesture on Windows. This change also handles the WM_POINTERDOWN

content/common/view_messages.h

 // Copyright (c) 2011 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 page rendering.
 // Multiply-included message file, hence no include guard.
 
 #include "base/process.h"
 #include "base/shared_memory.h"
 #include "content/common/content_export.h"
@@ skipping 902 matching lines @@
 // telling it what url got zoomed and what its current zoom level is.
 IPC_MESSAGE_ROUTED1(ViewMsg_Zoom,
                     content::PageZoom /* function */)
 
 // Set the zoom level for the current main frame.  If the level actually
 // changes, a ViewHostMsg_DidZoomURL message will be sent back to the browser
 // telling it what url got zoomed and what its current zoom level is.
 IPC_MESSAGE_ROUTED1(ViewMsg_SetZoomLevel,
                     double /* zoom_level */)
 
+// Zooms the page by the factor defined in the renderer.
+IPC_MESSAGE_ROUTED3(ViewMsg_ZoomFactor,
+                    content::PageZoom,
+                    int /* zoom center_x */,
+                    int /* zoom center_y */)
+
 // Set the zoom level for a particular url that the renderer is in the
 // process of loading.  This will be stored, to be used if the load commits
 // and ignored otherwise.
 IPC_MESSAGE_ROUTED2(ViewMsg_SetZoomLevelForLoadingURL,
                     GURL /* url */,
                     double /* zoom_level */)
 
 // Set the zoom level for a particular url, so all render views
 // displaying this url can update their zoom levels to match.
 IPC_MESSAGE_CONTROL2(ViewMsg_SetZoomLevelForCurrentURL,
@@ skipping 1005 matching lines @@
                      media::MediaLogEvent /* event */)
 
 // Requests to lock the mouse. Will result in a ViewMsg_LockMouse_ACK message
 // being sent back.
 IPC_MESSAGE_ROUTED0(ViewHostMsg_LockMouse)
 
 // Requests to unlock the mouse. A ViewMsg_MouseLockLost message will be sent
 // whenever the mouse is unlocked (which may or may not be caused by
 // ViewHostMsg_UnlockMouse).
 IPC_MESSAGE_ROUTED0(ViewHostMsg_UnlockMouse)