[Extensions Bindings] Request JS execution from messaging bindings

extensions/renderer/resources/messaging.js

 // Copyright 2014 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.
 
 // chrome.runtime.messaging API implementation.
 // TODO(robwu): Fix this indentation.
 
   // TODO(kalman): factor requiring chrome out of here.
   var chrome = requireNative('chrome').GetChrome();
   var lastError = require('lastError');
@@ skipping 229 matching lines @@
   function dispatchOnConnect(portId,
                              channelName,
                              sourceTab,
                              sourceFrameId,
                              guestProcessId,
                              guestRenderFrameRoutingId,
                              sourceExtensionId,
                              targetExtensionId,
                              sourceUrl,
                              tlsChannelId) {
+    var usedPort = dispatchOnConnectImpl(portId, channelName, sourceTab,
+                                         sourceFrameId, guestProcessId,
+                                         guestRenderFrameRoutingId,
+                                         sourceExtensionId, targetExtensionId,
+                                         sourceUrl, tlsChannelId);
+    if (!usedPort) {

[lazyboy, 2017/06/05 18:18:33]

nit: isPortUsed (usedPort var might be misleading to mean that it is the used
port).

[Devlin, 2017/06/09 20:18:02]

Good point; changed to wasPortUsed.

+      // Since the JS to dispatch the connect event can (in rare cases) be
+      // executed asynchronously from when we check if there are associated
+      // listeners in the native code, it's possible that the listeners have
+      // since been removed. If that's the case (though unlikely), remove the
+      // port.
+      messagingNatives.CloseChannel(portId, false);

[lazyboy, 2017/06/05 18:18:33]

nit: false /* force_close */

[Devlin, 2017/06/09 20:18:02]

Done.

+    }
+  }
+
+  // Helper function to dispatchOnConnect that returns true if the new port
+  // was used.
+  function dispatchOnConnectImpl(portId,
+                                 channelName,
+                                 sourceTab,
+                                 sourceFrameId,
+                                 guestProcessId,
+                                 guestRenderFrameRoutingId,
+                                 sourceExtensionId,
+                                 targetExtensionId,
+                                 sourceUrl,
+                                 tlsChannelId) {
     // Only create a new Port if someone is actually listening for a connection.
     // In addition to being an optimization, this also fixes a bug where if 2
     // channels were opened to and from the same process, closing one would
     // close both.
     var extensionId = processNatives.GetExtensionId();
 
     // messaging_bindings.cc should ensure that this method only gets called for
     // the right extension.
     logging.CHECK(targetExtensionId == extensionId);
 
@@ skipping 175 matching lines @@
 exports.$set('kNativeMessageChannel', kNativeMessageChannel);
 exports.$set('Port', Port);
 exports.$set('createPort', createPort);
 exports.$set('sendMessageImpl', sendMessageImpl);
 exports.$set('sendMessageUpdateArguments', sendMessageUpdateArguments);
 
 // For C++ code to call.
 exports.$set('dispatchOnConnect', dispatchOnConnect);
 exports.$set('dispatchOnDisconnect', dispatchOnDisconnect);
 exports.$set('dispatchOnMessage', dispatchOnMessage);