Move EarlGrey helper to check toolbar visibility into ChromeEarlGreyUI.

ios/chrome/test/earl_grey/chrome_earl_grey_ui.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_CHROME_TEST_EARL_GREY_CHROME_EARL_GREY_UI_H_
 #define IOS_CHROME_TEST_EARL_GREY_CHROME_EARL_GREY_UI_H_
 
 #import <Foundation/Foundation.h>
 
 // Test methods that perform actions on Chrome. These methods only affect Chrome
@@ skipping 11 matching lines @@
 // Open a new incognito tab via the tools menu.
 + (void)openNewIncognitoTab;
 
 // Reloads the page. Does not wait until reload finishes.
 + (void)reload;
 
 // Opens the share menu by tapping on the share button.
 // Requires having a tab opened.
 + (void)openShareMenu;
 
+// Waits for toolbar to become visible if |isVisible| is YES, or waits for it
+// to disappear if |isVisible| is NO. Induces a GREYAssert if the condition is
+// not met after a timeout.
++ (void)waitForToolbarVisible:(BOOL)isVisible;
+
 @end
 
 #endif  // IOS_CHROME_TEST_EARL_GREY_CHROME_EARL_GREY_UI_H_