First cut at "content handling" support in Mojo.

mojo/public/interfaces/service_provider/content_handler.mojom

Index: mojo/public/interfaces/service_provider/content_handler.mojom
diff --git a/mojo/public/interfaces/service_provider/content_handler.mojom b/mojo/public/interfaces/service_provider/content_handler.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..c8caf3106f6cfc2a56a579fb3f773dfb796ebb6d
--- /dev/null
+++ b/mojo/public/interfaces/service_provider/content_handler.mojom
@@ -0,0 +1,15 @@
+// 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.
+
+import "mojo/public/interfaces/service_provider/service_provider.mojom"
+
+module mojo {
+
+interface ContentHandler {
+  OnConnect(string url,
+            handle<data_pipe_consumer> content,

[darin (slow to review), 2014/08/03 06:12:02]

Are you thinking we can get away with not supplying the URLResponse here? Some
response headers (e.g., Content-Type) will matter to content handlers. An app
might be registered as a content handler for N mime types. It might also find
the charset hint from the response headers useful. But, perhaps it is possible
to provide something less than a full URLResponse data structure here.

Also, is it useful / good (from a security perspective) to provide the chain of
redirects to the content handler?

[Aaron Boodman, 2014/08/03 11:11:40]

No, we will need the full URLResponse or something close to it. I encountered
some dependency issues using it, changed it to this data pipe temporarily, then
forgot to go back and figure that out. I will look at it again, maybe in a
separate change.
I'm not sure. Currently I don't see anything in URLResponse that exposes the
redirect chain - am I missing it? Does Blink need the redirect chain for any
reason?

+            ServiceProvider service_provider);
+};
+
+}