Implement BroadcastChannel

components/webmessaging/public/interfaces/broadcast_channel.mojom

Index: components/webmessaging/public/interfaces/broadcast_channel.mojom
diff --git a/components/webmessaging/public/interfaces/broadcast_channel.mojom b/components/webmessaging/public/interfaces/broadcast_channel.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..e4e34926f68bf7113a386887b8993b86c2e01b4d
--- /dev/null
+++ b/components/webmessaging/public/interfaces/broadcast_channel.mojom
@@ -0,0 +1,24 @@
+// Copyright 2016 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.
+
+module webmessaging.mojom;
+
+import "url/mojo/origin.mojom";
+
+interface BroadcastChannelClient {

[dcheng, 2016/06/30 08:23:11]

Nit: can we add some sort of interface-level comment, e.g. the purpose of this
interface? Some sort of documentation about where the service is hosted would be
nice too (since this interface is implemented in both the trusted browser
process and the untrusted renderers)

[Marijn Kruisselbrink, 2016/06/30 17:21:56]

Added some explicit comments to this interface.

+  // Messages are passed as SerializedScriptValue.
+  OnMessage(string message);
+};
+
+interface BroadcastChannelProvider {

[dcheng, 2016/06/30 08:23:12]

Is there expected to be one of these in the browser per renderer? Or some other
model? I guess it's exposed by StoragePartition, but I don't know how that
concretely maps to the process model. Sorry if this is a dumb question =)

[Marijn Kruisselbrink, 2016/06/30 17:21:56]

A content::BrowserContext (chrome::Profile) consists of multiple
StoragePartition, and each renderer process lives inside a particular storage
partition (this is for example how chrome apps have separate cookie jars/storage
from regular websites).

So the way that's currently implemented is that there is one
BroadcastChannelProvider instance in the browser process for each
StoragePartition, and all connections from all renderers in that storage
partition end up binding to the same Provider implementation.

Added some more comments to explain this a bit more.

+  // Connect to the channel identified by the |origin| and |name|. Messages can
+  // be sent to the channel using |sender|, and messages to the channel will be
+  // received by |receiver|.
+  // All connections to channels made from the same event loop should be made
+  // through the same BroadcastChannelProvider to ensure correct ordering of
+  // messages.
+  ConnectToChannel(url.mojom.Origin origin, string name,
+                   associated BroadcastChannelClient receiver,
+                   associated BroadcastChannelClient& sender);
+};