Add a WebContentsImpl API to snapshot the accessibility tree.

content/common/accessibility_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 accessibility.
 // Multiply-included message file, hence no include guard.
 
 #include "base/basictypes.h"
 #include "content/common/content_export.h"
 #include "content/common/view_message_enums.h"
@@ skipping 160 matching lines @@
 // incoming accessibility IPCs until it receives one with the matching reset
 // token. Conversely, it ignores IPCs with a reset token if it was not
 // expecting a reset.
 IPC_MESSAGE_ROUTED1(AccessibilityMsg_Reset,
                     int /* reset token */)
 
 // Kill the renderer because we got a fatal error in the accessibility tree
 // and we've already reset too many times.
 IPC_MESSAGE_ROUTED0(AccessibilityMsg_FatalError)
 
+// Request a one-time snapshot of the accessibility tree without
+// enabling accessibility if it wasn't already enabled. The passed id
+// will be returned in the AccessibilityHostMsg_SnapshotResponse message.
+IPC_MESSAGE_ROUTED1(AccessibilityMsg_SnapshotTree,
+                    int /* request id */)
+
 // Messages sent from the renderer to the browser.
 
 // Sent to notify the browser about renderer accessibility events.
 // The browser responds with a AccessibilityMsg_Events_ACK.
 // The second parameter, reset_token, is set if this IPC was sent in response
 // to a reset request from the browser. When the browser requests a reset,
 // it ignores incoming IPCs until it sees one with the correct reset token.
 // Any other time, it ignores IPCs with a reset token.
 IPC_MESSAGE_ROUTED2(
     AccessibilityHostMsg_Events,
     std::vector<AccessibilityHostMsg_EventParams> /* events */,
     int /* reset_token */)
 
 // Sent to update the browser of the location of accessibility objects.
 IPC_MESSAGE_ROUTED1(
     AccessibilityHostMsg_LocationChanges,
     std::vector<AccessibilityHostMsg_LocationChangeParams>)
 
 // Sent to update the browser of the location of accessibility objects.
 IPC_MESSAGE_ROUTED1(
     AccessibilityHostMsg_FindInPageResult,
     AccessibilityHostMsg_FindInPageResultParams)
+
+// Sent in response to AccessibilityMsg_SnapshotTree. The request id that was
+// passed to the request will be returned in |request_id|, along with
+// a standalone snapshot of the accessibility tree.
+IPC_MESSAGE_ROUTED2(AccessibilityHostMsg_SnapshotResponse,
+                    int /* request_id */,
+                    ui::AXTreeUpdate)