Migrate mac installer to delegate-driven model

chrome/installer/mac/app/MainDelegate.m

+// 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.
+
+#import "MainDelegate.h"
+
+@implementation MainDelegate
+
+- (void)runApplication {
+  OmahaCommunication* messenger = [[OmahaCommunication alloc] init];
+  messenger.delegate = self;
+
+  [messenger sendRequest];
+}
+
+- (void)onOmahaSuccessWithResponseBody:(NSData*)responseBody
+                              AndError:(NSError*)error {
+  if (error) {
+    NSLog(@"error: %@", [error localizedDescription]);
+    exit(1);
+  }
+  Downloader* download = [[Downloader alloc] init];
+  download.delegate = self;
+
+  [download downloadChromeImageToDownloadsDirectory:responseBody];
+}
+
+- (void)onDownloadSuccess {
+  // TODO: replace the line of code below with real code someday to unpack dmg
+  exit(0);
+}
+
+- (void)onUnpackSuccess {
+}
+
+@end