Add helpers to swipe up and down on the current web view.

ios/chrome/browser/context_menu/context_menu_egtest.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 <EarlGrey/EarlGrey.h>
 #import <UIKit/UIKit.h>
 #import <XCTest/XCTest.h>
 
 #include "base/strings/sys_string_conversions.h"
 #include "ios/chrome/browser/ui/ui_util.h"
@@ skipping 191 matching lines @@
       "<div style='height:4000px'></div>"
       "<a style='margin-left:50px' href='" +
       destinationURL.spec() + "' id='link'>link</a>";
   responses[destinationURL] = kDestinationHtml;
 
   web::test::SetUpSimpleHttpServer(responses);
   [ChromeEarlGrey loadURL:initialURL];
   chrome_test_util::AssertMainTabCount(1U);
 
   // Scroll down on the web view to make the link visible.
-  [[EarlGrey
-      selectElementWithMatcher:WebViewScrollView(
-                                   chrome_test_util::GetCurrentWebState())]
-      performAction:grey_swipeFastInDirection(kGREYDirectionUp)];
+  [ChromeEarlGreyUI swipeUpOnWebView];
   [[EarlGrey selectElementWithMatcher:chrome_test_util::WebViewContainingText(
                                           kDestinationLinkID)]
       assertWithMatcher:grey_notNil()];
 
   LongPressElementAndTapOnButton(kDestinationLinkID, OpenLinkInNewTabButton());
 
   // Earl Grey cannot preperly synchronize some animations, so adding a
   // WaitUntilCondition to wait for the new tab opening animation to finish
   // and the scroll view to become interactable.
   ConditionBlock condition = ^{
     NSError* error = nil;
     [[EarlGrey
         selectElementWithMatcher:WebViewScrollView(
                                      chrome_test_util::GetCurrentWebState())]
         assertWithMatcher:grey_interactable()
                     error:&error];
     return !error;
   };
   GREYAssert(testing::WaitUntilConditionOrTimeout(
                  testing::kWaitForUIElementTimeout, condition),
              @"Web view did not become interactable");
 
   // Make the toolbar visible by scrolling up on the web view to select the
   // newly opened tab.
-  [[EarlGrey
-      selectElementWithMatcher:WebViewScrollView(
-                                   chrome_test_util::GetCurrentWebState())]
-      performAction:grey_swipeFastInDirection(kGREYDirectionDown)];
+  [ChromeEarlGreyUI swipeDownOnWebView];
   chrome_test_util::AssertToolbarVisible();
 
   SelectTabAtIndexInCurrentMode(1U);
 
   // Verify url and tab count.
   [[EarlGrey selectElementWithMatcher:chrome_test_util::OmniboxText(
                                           destinationURL.GetContent())]
       assertWithMatcher:grey_notNil()];
   chrome_test_util::AssertMainTabCount(2U);
 }
 
 @end