Add a mimeHandler extension API.

extensions/renderer/resources/mime_handler_private_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('mimeHandlerPrivate');
+
+var NO_STREAM_ERROR =
+    'Streams are only available from a mime handler view guest.';
+var STREAM_ABORTED_ERROR = 'Stream has been aborted.';
+
+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)));
+});
+
+// Stores a promise to the GetStreamInfo() result to avoid making additional
+// calls in response to getStreamInfo() calls.
+var streamInfoPromise;
+
+function throwError(error) {

[benwells, 2015/01/19 01:05:19]

Sorry this code makes me feel dumb. Why does throwError not throw an error but
return a function that will throw an error?

[Sam McNally, 2015/01/19 04:29:57]

Changed to not do this.

+  return function() {
+    throw new Error(error);
+  }
+}
+
+function createStreamInfoPromise() {
+  return servicePromise.then(function(service) {
+    return service.getStreamInfo();
+  }).then(function(result) {
+    if (!result.stream_info)
+      throw new Error(STREAM_ABORTED_ERROR);
+    return result.stream_info;
+  }, throwError(NO_STREAM_ERROR));
+}
+
+function constructStreamInfoDict(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,
+    embedded: !!streamInfo.embedded,
+    responseHeaders: headers,
+  };
+}
+
+binding.registerCustomHook(function(bindingsAPI) {
+  var apiFunctions = bindingsAPI.apiFunctions;
+  apiFunctions.setHandleRequestWithPromise('getStreamInfo', function() {
+    if (!streamInfoPromise)
+      streamInfoPromise = createStreamInfoPromise();
+    return streamInfoPromise.then(constructStreamInfoDict);
+  });
+
+  apiFunctions.setHandleRequestWithPromise('abortStream', function() {
+    return servicePromise.then(function(service) {
+      return service.abortStream().then(function() {});
+    }).catch(throwError(NO_STREAM_ERROR));
+  });
+});
+
+exports.binding = binding.generate();