Create ChromeEarlGrey waitForWebViewContainingText.

ios/web/shell/test/earl_grey/shell_earl_grey.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.
 
 #ifndef IOS_WEB_SHELL_TEST_EARL_GREY_SHELL_EARL_GREY_H_
 #define IOS_WEB_SHELL_TEST_EARL_GREY_SHELL_EARL_GREY_H_
 
 #import <Foundation/Foundation.h>
 
 #include "url/gurl.h"
 
 // Test methods that perform actions on Web Shell. These methods may read or
 // alter Web Shell's internal state programmatically or via the UI, but in both
 // cases will properly synchronize the UI for Earl Grey tests.
 @interface ShellEarlGrey : NSObject
 
 // Loads |URL| in the current WebState with transition of type
 // ui::PAGE_TRANSITION_TYPED, and waits for the page to complete loading, or
 // a timeout.
 + (void)loadURL:(const GURL&)URL;
 
+// Waits for the current web view to contain |text|. If the condition is not met
+// within a timeout, a GREYAssert is induced.
++ (void)waitForWebViewContainingText:(const std::string)text;
+
 @end
 
 #endif  // IOS_WEB_SHELL_TEST_EARL_GREY_SHELL_EARL_GREY_H_