Create ChromeEarlGrey waitForWebViewContainingText.

ios/web/shell/test/earl_grey/shell_earl_grey.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/earl_grey/shell_earl_grey.h"
 
 #import <EarlGrey/EarlGrey.h>
 
 #import "ios/testing/wait_util.h"
 #import "ios/web/public/test/earl_grey/js_test_util.h"
+#import "ios/web/public/test/web_view_content_test_util.h"
 #include "ios/web/shell/test/app/navigation_test_util.h"
 #import "ios/web/shell/test/app/web_shell_test_util.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @implementation ShellEarlGrey
 
 + (void)loadURL:(const GURL&)URL {
@@ skipping 12 matching lines @@
 
   web::WebState* webState = web::shell_test_util::GetCurrentWebState();
   if (webState->ContentIsHTML())
     web::WaitUntilWindowIdInjected(webState);
 
   // Ensure any UI elements handled by EarlGrey become idle for any subsequent
   // EarlGrey steps.
   [[GREYUIThreadExecutor sharedInstance] drainUntilIdle];
 }
 
++ (void)waitForWebViewContainingText:(std::string)text {
+  GREYCondition* condition = [GREYCondition
+      conditionWithName:@"Wait for web view containing text"
+                  block:^BOOL {
+                    return web::test::IsWebViewContainingText(
+                        web::shell_test_util::GetCurrentWebState(), text);
+                  }];
+  GREYAssert([condition waitWithTimeout:testing::kWaitForUIElementTimeout],
+             @"Failed waiting for web view containing %s", text.c_str());
+}
+
 @end