Tests fail due to adding subviews to visual view effect compatibility issues.  It happens on the web shell context menu but not the chrome one.  May need to refactor the web shell context menu when presenting alert views.

Failures:
Do not add subviews directly to the visual effect view itself, instead add them to the -contentView.

Tests fail from the matcher ContextMenuItemWithText.

Yuke has the fix for a similar test fail, assigning to liaoyuke@.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2b324b9670c04b3fc20e92f6eca4a177913aea66

commit 2b324b9670c04b3fc20e92f6eca4a177913aea66
Author: Yuke Liao <liaoyuke@chromium.org>
Date: Fri Jul 28 03:06:03 2017

Fix context menu egtests on iOS 11.

EarlGrey has a weird bug on iOS 11 when trying to match and tap a
_UIAlertControllerView using grey_ancestor. This CL fixes those broken 
tests to not use grey_ancestor, which I think also makes the helper 
function cleaner.

Bug:  747439 ,  748122 
Change-Id: I4465d7a57086e505522c3039bbe4256b5101c077
Reviewed-on: https://chromium-review.googlesource.com/590652
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Mike Baxley <baxley@chromium.org>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490232}
[modify] https://crrev.com/2b324b9670c04b3fc20e92f6eca4a177913aea66/ios/chrome/browser/ui/dialogs/javascript_dialog_egtest.mm
[modify] https://crrev.com/2b324b9670c04b3fc20e92f6eca4a177913aea66/ios/testing/earl_grey/matchers.h
[modify] https://crrev.com/2b324b9670c04b3fc20e92f6eca4a177913aea66/ios/testing/earl_grey/matchers.mm
[modify] https://crrev.com/2b324b9670c04b3fc20e92f6eca4a177913aea66/ios/web/shell/test/context_menu_egtest.mm