Update IPC browser_plugin_instance_id before sending queued messages

content/browser/browser_plugin/browser_plugin_guest.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/browser_plugin/browser_plugin_guest.h"
 
 #include <algorithm>
 
 #include "base/message_loop/message_loop.h"
 #include "base/pickle.h"
@@ skipping 546 matching lines @@
     seen_embedder_drag_source_ended_at_ = false;
     dragged_url_ = GURL();
   }
 }
 
 void BrowserPluginGuest::EmbedderSystemDragEnded() {
   seen_embedder_system_drag_ended_ = true;
   EndSystemDragIfApplicable();
 }
 
+// TODO(wjmaclean): Replace this approach with ones based on std::function
+// as in https://codereview.chromium.org/1404353004/ once all Chrome platforms
+// support this. https://crbug.com/544212
+IPC::Message* BrowserPluginGuest::UpdateInstanceIdIfNecessary(
+    IPC::Message* msg) const {
+  DCHECK(msg);
+
+  int msg_browser_plugin_instance_id = browser_plugin::kInstanceIDNone;
+  base::PickleIterator iter(*msg);
+  if (!iter.ReadInt(&msg_browser_plugin_instance_id) ||
+      msg_browser_plugin_instance_id != browser_plugin::kInstanceIDNone) {
+    return msg;
+  }
+
+  // This method may be called with no browser_plugin_instance_id in tests.
+  if (!browser_plugin_instance_id())
+    return msg;
+
+  scoped_ptr<IPC::Message> new_msg(
+      new IPC::Message(msg->routing_id(), msg->type(), msg->priority()));
+  new_msg->WriteInt(browser_plugin_instance_id());
+
+  // Copy remaining payload from original message.
+  // TODO(wjmaclean): it would be nice if IPC::PickleIterator had a method
+  // like 'RemainingBytes()' so that we don't have to include implementation-
+  // specific details like sizeof() in the next line.
+  DCHECK(msg->payload_size() > sizeof(int));
+  size_t remaining_bytes = msg->payload_size() - sizeof(int);
+  const char* data = nullptr;
+  CHECK(iter.ReadBytes(&data, remaining_bytes))

[lfg, 2015/10/16 18:25:49]

It's not a good idea to have the code inside the CHECK() (if someone ever tries
to compile without checks, it makes it very hard to find why it doesn't work),
please move it outside.

[lazyboy, 2015/10/16 18:27:15]

+1 Thanks for noticing this.

+      << "Unexpected failure reading remaining IPC::Message payload.";
+  CHECK(new_msg->WriteBytes(data, remaining_bytes))
+      << "Unexpected failure writing remaining IPC::Message payload.";
+
+  delete msg;
+  return new_msg.release();
+}
+
 void BrowserPluginGuest::SendQueuedMessages() {
   if (!attached())
     return;
 
   while (!pending_messages_.empty()) {
     linked_ptr<IPC::Message> message_ptr = pending_messages_.front();
     pending_messages_.pop_front();
-    SendMessageToEmbedder(message_ptr.release());
+    SendMessageToEmbedder(
+        UpdateInstanceIdIfNecessary(message_ptr.release()));
   }
 }
 
 void BrowserPluginGuest::SendTextInputTypeChangedToView(
     RenderWidgetHostViewBase* guest_rwhv) {
   if (!guest_rwhv)
     return;
 
   if (!owner_web_contents_) {
     // If we were showing an interstitial, then we can end up here during
@@ skipping 426 matching lines @@
           range, character_bounds);
 }
 #endif
 
 void BrowserPluginGuest::SetContextMenuPosition(const gfx::Point& position) {
   if (delegate_)
     delegate_->SetContextMenuPosition(position);
 }
 
 }  // namespace content