Implement sync protocol changes

Update protobuf definitions and refactor message receive and decrypt
codepath to support new protocol, including various flavors of sync
messages (sent messages, contacts, and groups).

Also cleans up background.js and lets libtextsecure internalize
textsecure.processDecrypted and ensure that it is called before handing
DataMessages off to the application.

The Envelope structure now has a generic content field and a
legacyMessage field for backwards compatibility. We'll send outgoing
messages as legacy messages, and sync messages as "content" while
continuing to support both legacy and non-legacy messages on the receive
side until old clients have a chance to transition.

libtextsecure/test/message_receiver_test.js

@@ -0,0 +1,50 @@
+/* vim: ts=4:sw=4:expandtab
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+describe('MessageReceiver', function() {
+    var WebSocket = window.WebSocket;
+    before(function() { window.WebSocket = MockSocket; });
+    after (function() { window.WebSocket = WebSocket;  });
+    it('connects', function(done) {
+        var mockServer = new MockServer('ws://localhost:8080');
+        var attrs = {
+            type: textsecure.protobuf.Envelope.Type.PLAINTEXT,
+            source: '+19999999999',
+            sourceDevice: '1',
+            timestamp: Date.now(),
+        };
+        mockServer.on('connection', function(server) {
+            var signal = new textsecure.protobuf.Envelope(attrs);
+            signal.message = new textsecure.protobuf.DataMessage({ body: 'hello' });
+            server.send(
+                new textsecure.protobuf.WebSocketMessage({
+                    type: textsecure.protobuf.WebSocketMessage.Type.REQUEST,
+                    request: { verb: 'PUT', path: '/messages', body: signal }
+                }).encode().toArrayBuffer()
+            );
+        });
+
+        window.addEventListener('signal', function(ev) {
+            var signal = ev.proto;
+            for (var key in attrs) {
+                assert.strictEqual(attrs[key], signal[key]);
+            }
+            assert.strictEqual(signal.message.body, 'hello');
+        });
+        var messageReceiver = new textsecure.MessageReceiver(window);
+        messageReceiver.connect();
+    });
+});