Update IPC browser_plugin_instance_id before sending queued messages

content/browser/browser_plugin/browser_plugin_guest.cc

Index: content/browser/browser_plugin/browser_plugin_guest.cc
diff --git a/content/browser/browser_plugin/browser_plugin_guest.cc b/content/browser/browser_plugin/browser_plugin_guest.cc
index 00529ffab22904afb2517c11d4d8eac2b82d20e6..a10565b2da70a8f5fc740f6865aed8c72cad48a6 100644
--- a/content/browser/browser_plugin/browser_plugin_guest.cc
+++ b/content/browser/browser_plugin/browser_plugin_guest.cc
@@ -564,6 +564,44 @@ void BrowserPluginGuest::EmbedderSystemDragEnded() {
   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;
@@ -571,7 +609,8 @@ void BrowserPluginGuest::SendQueuedMessages() {
   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()));
   }
 }