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

ios/chrome/browser/context_menu/context_menu_egtest.mm

Index: ios/chrome/browser/context_menu/context_menu_egtest.mm
diff --git a/ios/chrome/browser/context_menu/context_menu_egtest.mm b/ios/chrome/browser/context_menu/context_menu_egtest.mm
index 923a41ed8126b9f97ce4a1d10439a39cdcad8989..2199db3440abb85e5cd39399956b26356e4477bf 100644
--- a/ios/chrome/browser/context_menu/context_menu_egtest.mm
+++ b/ios/chrome/browser/context_menu/context_menu_egtest.mm
@@ -209,10 +209,7 @@ void SelectTabAtIndexInCurrentMode(NSUInteger index) {
   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()];
@@ -237,10 +234,7 @@ void SelectTabAtIndexInCurrentMode(NSUInteger index) {
 
   // 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);