Add a mimeHandler extension API.

extensions/renderer/resources/mime_handler_custom_bindings.js

+// Copyright 2015 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.
+
+/**
+ * Custom bindings for the mime handler API.
+ */
+
+var binding = require('binding').Binding.create('mimeHandler');
+
+var NO_STREAM_ERROR =
+    'Streams are only available from a mime handler view guest';
+var STREAM_ABORTED_ERROR = 'Stream has been aborted';

[raymes, 2015/01/12 05:26:04]

nit: should we add full stops to these messages?

[Sam McNally, 2015/01/12 07:13:35]

Done.

+
+var servicePromise = Promise.all([
+    requireAsync('content/public/renderer/service_provider'),
+    requireAsync('extensions/common/api/mime_handler.mojom'),
+    requireAsync('mojo/public/js/router'),
+]).then(function(modules) {
+  var serviceProvider = modules[0];
+  var mojom = modules[1];
+  var routerModule = modules[2];
+  return new mojom.MimeHandlerService.proxyClass(new routerModule.Router(
+      serviceProvider.connectToService(mojom.MimeHandlerService.name)));
+});
+
+var streamInfoPromise;

[raymes, 2015/01/13 00:05:11]

Do we really need to store this promise? Would it hurt to reconstruct it for
each call, assuming there are a small number of calls?

[Sam McNally, 2015/01/13 05:30:08]

Added a comment on what this caches and why.

+
+function populateStreamInfo() {

[raymes, 2015/01/13 00:05:10]

Can this be called createStreamInfoPromise?

[Sam McNally, 2015/01/13 05:30:08]

Done.

+  streamInfoPromise = servicePromise.then(function(service) {
+    return service.getStreamInfo();
+  }).then(function(result) {
+    if (!result.stream_info)
+      throw new Error(STREAM_ABORTED_ERROR);
+    return result.stream_info;
+  }, function(error) {
+    throw new Error(NO_STREAM_ERROR);
+  });

[raymes, 2015/01/13 00:05:11]

Can we pull this apart a bit? Like

serviecPromise.then(getStreamInfo)
                       .then(returnStreamInfo, noStreamError);

[Sam McNally, 2015/01/13 05:30:08]

Done for the error case. I think the normal case is fairly reasonable.

+}
+
+binding.registerCustomHook(function(bindingsAPI) {
+  var apiFunctions = bindingsAPI.apiFunctions;
+  apiFunctions.setHandleRequestWithPromise('getStreamInfo', function() {
+    if (!streamInfoPromise)
+      populateStreamInfo();

[raymes, 2015/01/13 00:05:10]

If you returned the promise in the function you could change this line to
streamInfoPromise = createStreamInfoPromise();

[Sam McNally, 2015/01/13 05:30:08]

Done.

+    return streamInfoPromise.then(function(streamInfo) {
+      var headers = {};
+      for (var header of streamInfo.response_headers) {
+        headers[header[0]] = header[1];
+      }
+      return {
+        mimeType: streamInfo.mime_type,
+        originalUrl: streamInfo.original_url,
+        streamUrl: streamInfo.stream_url,
+        tabId: streamInfo.tab_id,
+        expectedContentSize: streamInfo.expected_content_size,
+        embedded: !!streamInfo.embedded,
+        responseHeaders: headers,
+      };
+    });
+  });
+
+  apiFunctions.setHandleRequestWithPromise('abortStream', function() {
+    return servicePromise.then(function(service) {
+      return service.abortStream().then(function() {}, function() {
+        throw new Error(NO_STREAM_ERROR);
+      });
+    });
+  });
+});
+
+exports.binding = binding.generate();