Move ImageFetcher to its own target.

ios/chrome/browser/net/image_fetcher/mock_image_fetcher.mm

 // 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.
 
-#import "ios/chrome/browser/net/mock_image_fetcher.h"
+#import "ios/chrome/browser/net/image_fetcher/mock_image_fetcher.h"
 
 MockImageFetcher::MockImageFetcher(
     const scoped_refptr<base::TaskRunner>& task_runner)
-    : ImageFetcher(task_runner) {
-}
+    : ImageFetcher(task_runner) {}
 
-MockImageFetcher::~MockImageFetcher() {
-}
+MockImageFetcher::~MockImageFetcher() {}