Make testContextMenuOpenInNewTabFromTallPage less flaky.

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 190 matching lines @@
   responses[initialURL] =
       "<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 sure the toolbar disappears.
+  [[EarlGrey
+      selectElementWithMatcher:WebViewScrollView(
+                                   chrome_test_util::GetCurrentWebState())]
+      performAction:grey_swipeFastInDirection(kGREYDirectionUp)];

[Eugene But (OOO till 7-30), 2017/03/13 22:35:01]

Instead of scrolling twice should we keep scrolling until hit the bottom?

[baxley, 2017/03/13 22:43:41]

This API does (or should) scroll to the bottom. I'll debug a little more. When
it failed, it looked like there was about one toolbar's worth of content to
scroll more to go. I am wondering if the timing of when the toolbar goes away is
messing with the calculation EG is using to find the bottom.

[Eugene But (OOO till 7-30), 2017/03/13 22:54:28]

Maybe this is because WebView's height has changed after the scrolling has
started?

[baxley, 2017/03/14 23:32:10]

Yes, that's my guess. This method is used in fullscreen_egtest (and maybe other
places) to hide the toolbar, maybe I'll make a helper for it. It seems
relatively reliable.

What do you think if I make the following changes?
- add a call to [ChromeEarlGreyUI waitForToolbarVisible:NO] after the first
swipe.
- Create a helper (swipeWebViewToHideToolbar), and then call that in place of
the first swipe. Even if it's calling the same EG method this will make it more
readable, and it will also allow us to come up with a better solution or change
implementation of how we hide the toolbar.

+
   // Scroll down on the web view to make the link visible.
   [[EarlGrey
       selectElementWithMatcher:WebViewScrollView(
                                    chrome_test_util::GetCurrentWebState())]
       performAction:grey_swipeFastInDirection(kGREYDirectionUp)];
   [[EarlGrey selectElementWithMatcher:chrome_test_util::WebViewContainingText(
                                           kDestinationLinkID)]
       assertWithMatcher:grey_notNil()];
 
   LongPressElementAndTapOnButton(kDestinationLinkID, OpenLinkInNewTabButton());
@@ skipping 25 matching lines @@
   SelectTabAtIndexInCurrentMode(1U);
 
   // Verify url and tab count.
   [[EarlGrey selectElementWithMatcher:chrome_test_util::OmniboxText(
                                           destinationURL.GetContent())]
       assertWithMatcher:grey_notNil()];
   chrome_test_util::AssertMainTabCount(2U);
 }
 
 @end