Get signals working in the EXTRA_DATA section of MHTML

content/common/frame_messages.h

 // Copyright 2013 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 interacting with frames.
 // Multiply-included message file, hence no include guard.
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 492 matching lines @@
   // disclosing uris to other renderer processes;  the digests should be
   // generated using SHA256HashString function from crypto/sha2.h and hashing
   // |salt + url.spec()|.
   IPC_STRUCT_MEMBER(std::set<std::string>, digests_of_uris_to_skip)
 
   // Salt used for |digests_of_uris_to_skip|.
   IPC_STRUCT_MEMBER(std::string, salt)
 
   // If |is_last_frame| is true, then an MHTML footer will be generated.
   IPC_STRUCT_MEMBER(bool, is_last_frame)
+
+  // Extra data to include in the MHTML file (used for tracking signal data).
+  IPC_STRUCT_MEMBER(std::vector<std::string>, extra_data)
+
 IPC_STRUCT_END()
 
 // This message is used to send hittesting data from the renderer in order
 // to perform hittesting on the browser process.
 IPC_STRUCT_BEGIN(FrameHostMsg_HittestData_Params)
   // |surface_id| represents the surface used by this remote frame.
   IPC_STRUCT_MEMBER(cc::SurfaceId, surface_id)
 
   // If |ignored_for_hittest| then this surface should be ignored during
   // hittesting.
@@ skipping 1040 matching lines @@
 // nearest find result in the sending frame.
 IPC_MESSAGE_ROUTED2(FrameHostMsg_GetNearestFindResult_Reply,
                     int /* nfr_request_id */,
                     float /* distance */)
 #endif
 
 // Adding a new message? Stick to the sort order above: first platform
 // independent FrameMsg, then ifdefs for platform specific FrameMsg, then
 // platform independent FrameHostMsg, then ifdefs for platform specific
 // FrameHostMsg.