Migrate mac installer to delegate-driven model

chrome/installer/mac/app/DownloadDelegate.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 <assert.h>
-
-#import "DownloadDelegate.h"
-#import "Downloader.h"
-
-@implementation DownloadDelegate : NSObject
-
-// Skeleton of delegate method to provide download progress updates.
-// TODO: Make use of (totalBytesWritten/totalBytesExpectedToWrite)*100
-// to generate download progress percentage.
-- (void)URLSession:(NSURLSession*)session
-                 downloadTask:(NSURLSessionDownloadTask*)downloadTask
-                 didWriteData:(int64_t)bytesWritten
-            totalBytesWritten:(int64_t)totalBytesWritten
-    totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {
-}
-
-// Delegate method to move downloaded disk image to user's Download directory.
-- (void)URLSession:(NSURLSession*)session
-                 downloadTask:(NSURLSessionDownloadTask*)downloadTask
-    didFinishDownloadingToURL:(NSURL*)location {
-  assert([location isFileURL]);
-  NSFileManager* manager = [[NSFileManager alloc] init];
-  NSURL* downloadsDirectory =
-      [[NSURL alloc] initFileURLWithPath:[Downloader getDownloadsFilePath]];
-  if ([manager fileExistsAtPath:location.path]) {
-    [manager copyItemAtURL:location toURL:downloadsDirectory error:nil];
-  } else {
-    // TODO: Error Handling
-  }
-}
-
-- (void)URLSession:(NSURLSession*)session
-                    task:(NSURLSessionTask*)task
-    didCompleteWithError:(NSError*)error {
-  // TODO: Error Handling
-}
-@end