Issue 916732  has been merged into this issue.

+marq@chromium.org, It looks like your https://chromium-review.googlesource.com/c/chromium/src/+/1382435 might have caused this. Mind taking a look?

reassigning to jochen@chromium.org, as their CL (https://chromium-review.googlesource.com/c/chromium/src/+/1374985) looks more likely 

[Sheriff] Removing Sheriff-Chromium label as the bug is assigned. Please re-add if you think it's unrelated.

i'd be surprised if my CL caused this. I added the trybot to the reland, and the test passed..

I looked at three recent failures, and found ContentSuggestionsTestCase/testOpenPageAndGoBackWithMoreContent is the failing tests in those three builds:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/ios-slimnav/1184
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/ios-slimnav/1182
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/ios-slimnav/1177


== copy of the failure log ==
../../ios/chrome/browser/ui/content_suggestions/content_suggestions_egtest.mm:313: error: -[ContentSuggestionsTestCase testOpenPageAndGoBackWithMoreContent] : Exception: AssertionFailedException

Exception Name: AssertionFailedException
Exception Reason: An assertion failed.
Exception with Assertion: {
  "Assertion Criteria":  "assertWithMatcher:CSHeader has correct offset: -210",
  "Element Matcher":  "(respondsToSelector(accessibilityIdentifier) && accessibilityID('CSHeaderIdentifier'))"
}

Exception Details: Error Trace: [
  {
    "Description":  "Assertion with matcher [M] failed: UI element [E] failed to match the following matcher(s): [S]",
    "Description Glossary":    {
      "M":  "CSHeader has correct offset: -210",
      "E":  "<ContentSuggestionsHeaderCell:0x7fdf1c23cb50; AX=N; AX.id='CSHeaderIdentifier'; AX.frame={{0, -214}, {375, 296}}; AX.activationPoint={187.5, -66}; AX.traits='UIAccessibilityTraitHeader'; AX.focused='N'; frame={{0, 112}, {375, 296}}; opaque; alpha=1>",
      "S":  "CSHeader has correct offset: -210"
    },
    "Error Domain":  "com.google.earlgrey.ElementInteractionErrorDomain",
    "Error Code":  "3",
    "File Name":  "GREYAssertions.m",
    "Function Name":  "+[GREYAssertions grey_createAssertionWithMatcher:]_block_invoke",
    "Line":  "75",
    "TestCase Class":  "ContentSuggestionsTestCase",
    "TestCase Method":  "testOpenPageAndGoBackWithMoreContent"
  }
]

At least these two tests are flaky according to the flakiness dashboard:
ContentSuggestionsTestCase/testOpenPageAndGoBackWithMoreContent
ContentSuggestionsTestCase/testMostVisitedRemoveUndo

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=ios_chrome_ui_egtests&tests=ContentSuggestionsTestCase

Gauthier: Assigned to you as a person who touched the code the most recently.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/43ba8e63298feeea7138694376f65cb93729e754

commit 43ba8e63298feeea7138694376f65cb93729e754
Author: Gauthier Ambard <gambard@chromium.org>
Date: Fri Dec 28 14:09:08 2018

[iOS] Remove test for header offset

This CL removes the test for the checking the header offset after coming
back to the NTP. This test is flaky and isn't really testing something
useful.

Bug:  916731 
Change-Id: Id0dbb924f2a4a2a11493c208ffbac73abf6d2bc8
Reviewed-on: https://chromium-review.googlesource.com/c/1391680
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619149}
[modify] https://crrev.com/43ba8e63298feeea7138694376f65cb93729e754/ios/chrome/browser/ui/content_suggestions/content_suggestions_egtest.mm
[modify] https://crrev.com/43ba8e63298feeea7138694376f65cb93729e754/ios/chrome/browser/ui/content_suggestions/ntp_home_test_utils.h
[modify] https://crrev.com/43ba8e63298feeea7138694376f65cb93729e754/ios/chrome/browser/ui/content_suggestions/ntp_home_test_utils.mm

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8a40c4dab2a550cf3e5c6581998b3be7432d4e00

commit 8a40c4dab2a550cf3e5c6581998b3be7432d4e00
Author: Gauthier Ambard <gambard@chromium.org>
Date: Fri Dec 28 14:14:58 2018

[iOS] Add delay to check NTP tile undo action

This CL adds a delay to the EarlGrey test that checks that the NTP Most
Visited tile is added back after hitting "undo" on the snackbar.

Bug:  916731 
Change-Id: I4bf425bfe42c85131dd9e89f1a5c9268fe261837
Reviewed-on: https://chromium-review.googlesource.com/c/1391681
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619150}
[modify] https://crrev.com/8a40c4dab2a550cf3e5c6581998b3be7432d4e00/ios/chrome/browser/ui/content_suggestions/content_suggestions_egtest.mm