Get signals working in the EXTRA_DATA section of MHTML

content/browser/download/mhtml_generation_manager.cc

 // 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.
 
 #include "content/browser/download/mhtml_generation_manager.h"
 
 #include <map>
 #include <queue>
 #include <utility>
 
@@ skipping 214 matching lines @@
   observed_renderer_process_host_.Add(rfh->GetProcess());
 
   // Tell the renderer to skip (= deduplicate) already covered MHTML parts.
   ipc_params.salt = salt_;
   ipc_params.digests_of_uris_to_skip = digests_of_already_serialized_uris_;
 
   ipc_params.destination_file = IPC::GetPlatformFileForTransit(
       browser_file_.GetPlatformFile(), false);  // |close_source_handle|.
   ipc_params.frame_routing_id_to_content_id =
       CreateFrameRoutingIdToContentId(rfh->GetSiteInstance());
+  if (params_.extra_data.size() > 0) {
+    // TODO(petewil): only need this on the main frame. How do I check which
+    // frame this is?
+    ipc_params.extra_data = params_.extra_data;

[fgorski, 2017/02/07 22:06:08]

do we really want to pass the data over IPC?
Did you consider appending to the file when it is already written?

(This implies handling the file size appropriately as well)

+  }
 
   // Send the IPC asking the renderer to serialize the frame.
   DCHECK_EQ(FrameTreeNode::kFrameTreeNodeInvalidId,
             frame_tree_node_id_of_busy_frame_);
   frame_tree_node_id_of_busy_frame_ = frame_tree_node_id;
   rfh->Send(new FrameMsg_SerializeAsMHTML(rfh->GetRoutingID(), ipc_params));
   TRACE_EVENT_NESTABLE_ASYNC_BEGIN1("page-serialization", "WaitingOnRenderer",
                                     this, "frame tree node id",
                                     frame_tree_node_id);
   DCHECK(wait_on_renderer_start_time_.is_null());
@@ skipping 300 matching lines @@
   return iter->second.get();
 }
 
 void MHTMLGenerationManager::RenderProcessExited(Job* job) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   DCHECK(job);
   JobFinished(job, MhtmlSaveStatus::RENDER_PROCESS_EXITED);
 }
 
 }  // namespace content