Refactor Assert[No]CookieExists to return a boolean

ios/chrome/test/earl_grey/chrome_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_CHROME_TEST_EARL_GREY_CHROME_EARL_GREY_H_
 #define IOS_CHROME_TEST_EARL_GREY_CHROME_EARL_GREY_H_
 
 #import <EarlGrey/EarlGrey.h>
 
 #include "url/gurl.h"
@@ skipping 16 matching lines @@
 // Test methods that perform actions on Chrome. These methods may read or alter
 // Chrome's internal state programmatically or via the UI, but in both cases
 // will properly synchronize the UI for Earl Grey tests.
 @interface ChromeEarlGrey : NSObject
 
 #pragma mark - History Utilities
 
 // Clears browsing history.
 + (void)clearBrowsingHistory;
 
+#pragma mark - Cookie Utilities
+
+// Returns cookies as key value pairs, where key is a cookie name and value is a
+// cookie value.
+// NOTE: this method fails the test if there are errors getting cookies.
++ (NSDictionary*)cookies;
+
 #pragma mark - Navigation Utilities
 
 // 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:(GURL)URL;
 
 // Waits for the page to finish loading or a timeout.
 + (void)waitForPageToFinishLoading;
 
 // Taps html element with |elementID| in the current web view.
 + (void)tapWebViewElementWithID:(NSString*)elementID;
 
 @end
 
 #endif  // IOS_CHROME_TEST_EARL_GREY_CHROME_EARL_GREY_H_