Refactor web shell integration tests utilities.

ios/web/shell/test/earl_grey/shell_matchers.h

 // 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 <EarlGrey/EarlGrey.h>
 
 namespace web {
 
+// Shorthand for GREYMatchers::matcherForWebViewContainingText.
+id<GREYMatcher> webViewContainingText(NSString* text);
+
 // Shorthand for GREYMatchers::matcherForBackButton.
 id<GREYMatcher> backButton();
 
 // Shorthand for GREYMatchers::matcherForForwardButton.
 id<GREYMatcher> forwardButton();
 
 // Shorthand for GREYMatchers::matcherForAddressField.
 id<GREYMatcher> addressField();
 
 }  // namespace web
 
 @interface GREYMatchers (WebShellAdditions)
 
+// Matcher for WKWebView containing |text|.
++ (id<GREYMatcher>)matcherForWebViewContainingText:(NSString*)text;
+
 // Matcher for back button in web shell.
 + (id<GREYMatcher>)matcherForWebShellBackButton;
 
 // Matcher for forward button in web shell.
 + (id<GREYMatcher>)matcherForWebShellForwardButton;
 
 // Matcher for address field in web shell.
 + (id<GREYMatcher>)matcherForWebShellAddressField;
 
 @end