Refactor web shell integration tests utilities.

ios/web/shell/test/shell_matchers.mm

-// 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 "ios/web/shell/test/shell_matchers.h"
-
-#import "ios/web/shell/view_controller.h"
-
-namespace web {
-
-id<GREYMatcher> backButton() {
-  return [GREYMatchers matcherForWebShellBackButton];
-}
-
-id<GREYMatcher> forwardButton() {
-  return [GREYMatchers matcherForWebShellForwardButton];
-}
-
-id<GREYMatcher> addressField() {
-  return [GREYMatchers matcherForWebShellAddressField];
-}
-
-}  // namespace web
-
-@implementation GREYMatchers (WebShellAdditions)
-
-+ (id<GREYMatcher>)matcherForWebShellBackButton {
-  return grey_accessibilityLabel(kWebShellBackButtonAccessibilityLabel);
-}
-
-+ (id<GREYMatcher>)matcherForWebShellForwardButton {
-  return grey_accessibilityLabel(kWebShellForwardButtonAccessibilityLabel);
-}
-
-+ (id<GREYMatcher>)matcherForWebShellAddressField {
-  return grey_accessibilityLabel(kWebShellAddressFieldAccessibilityLabel);
-}
-
-@end