Tests are failing for a few different reasons.  The failures alternate, so I'm guessing that the first error is the real issue, and the second is what happens when a Fullscreen test tries to run after the previous test did not complete and clean up properly.

Ideally we'd fix the underlying issue and also fix tests to pass even if the previous test failed.

***************************************************

-[FullscreenTestCase testChromeToChromeURLKeepsHeaderOnScreen]
-[FullscreenTestCase testShowHeaderOnErrorPage]
-[FullscreenTestCase testShowHeaderOnRegularPageLoad]

2018-05-09 19:52:05.046 ios_chrome_ui_egtests[19247:323619] -[NSNull grey_setAnimationState:]: unrecognized selector sent to instance 0x115e37ef0
<unknown>:0: error: -[FullscreenTestCase testChromeToChromeURLKeepsHeaderOnScreen] : failed: caught "NSInvalidArgumentException", "-[NSNull grey_setAnimationState:]: unrecognized selector sent to instance 0x115e37ef0"
(
	0   CoreFoundation                      0x0000000115b6e12b __exceptionPreprocess + 171
	1   libobjc.A.dylib                     0x000000011b45df41 objc_exception_throw + 48
	2   CoreFoundation                      0x0000000115bef024 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132
	3   CoreFoundation                      0x0000000115af0f78 ___forwarding___ + 1432
	4   CoreFoundation                      0x0000000115af0958 _CF_forwarding_prep_0 + 120
	5   EarlGrey                            0x0000000119147e67 AnimationDidStop + 151
	6   EarlGrey                            0x0000000119147f8e -[GREYCAAnimationDelegate greyswizzled_animationDidStop:finished:] + 94
	7   UIKit                               0x0000000114688065 __63-[UIViewPropertyAnimator finalizeStoppedAnimationWithPosition:]_block_invoke.999 + 451
	8   UIKit                               0x0000000114687d48 -[UIViewPropertyAnimator finalizeStoppedAnimationWithPosition:] + 796
	9   UIKit                               0x0000000114681a3c -[UIViewPropertyAnimator _runCompletions:finished:] + 37
	10  ios_chrome_ui_egtests               0x00000001075fe1ee -[FullscreenAnimator stopAnimation:] + 190
	11  ios_chrome_ui_egtests               0x00000001075eeaa1 _ZN18FullscreenMediator12StopAnimatorEPU8__strongP18FullscreenAnimatorb + 417
	12  ios_chrome_ui_egtests               0x00000001075ed904 _ZN18FullscreenMediator13StopAnimatingEb + 516
	13  ios_chrome_ui_egtests               0x00000001075ee1f7 _ZN18FullscreenMediator23FullscreenModelWasResetEP15FullscreenModel + 39
	14  ios_chrome_ui_egtests               0x00000001075f4925 _ZN15FullscreenModel18ResetForNavigationEv + 293
	15  ios_chrome_ui_egtests               0x00000001075fc6f1 _ZN26FullscreenWebStateObserver19DidFinishNavigationEPN3web8WebStateEPNS0_17NavigationContextE + 529
	16  ios_chrome_ui_egtests               0x0000000106e4f7d0 _ZN3web12WebStateImpl20OnNavigationFinishedEPNS_17NavigationContextE + 368
	17  ios_chrome_ui_egtests               0x0000000106ec1e22 -[CRWWebController webView:didCommitNavigation:] + 5506
	18  WebKit                              0x00000001192b4e5b _ZN6WebKit15NavigationState16NavigationClient19didCommitNavigationERNS_12WebPageProxyEPN3API10NavigationEPNS4_6ObjectE + 91
	19  WebKit                              0x0000000119414fd7 _ZN6WebKit12WebPageProxy21didCommitLoadForFrameEyyRKN3WTF6StringEbjRKN7WebCore15CertificateInfoEbSt8optionalINS5_18HasInsecureContentEERKNS_8UserDataE + 607
	20  WebKit                              0x0000000119438266 _ZN3IPC22callMemberFunctionImplIN6WebKit12WebPageProxyEMS2_FvyyRKN3WTF6StringEbjRKN7WebCore15CertificateInfoEbSt8optionalINS7_18HasInsecureContentEERKNS1_8UserDataEENSt3__15tupleIJyyS4_bjS8_bSD_SE_EEEJLm0ELm1ELm2ELm3ELm4ELm5ELm6ELm7ELm8EEEEvPT_T0_OT1_NSJ_16integer_sequenceImJXspT2_EEEE + 108
	21  WebKit                              0x0000000119431bd2 _ZN3IPC13handleMessageIN8Messages12WebPageProxy21DidCommitLoadForFrameEN6WebKit12WebPageProxyEMS5_FvyyRKN3WTF6StringEbjRKN7WebCore15CertificateInfoEbSt8optionalINSA_18HasInsecureContentEERKNS4_8UserDataEEEEvRNS_7DecoderEPT0_T1_ + 109
	22  WebKit                              0x00000001192b1801 _ZN3IPC18MessageReceiverMap15dispatchMessageERNS_10ConnectionERNS_7DecoderE + 127
	23  WebKit                              0x00000001194842da _ZN6WebKit15WebProcessProxy17didReceiveMessageERN3IPC10ConnectionERNS1_7DecoderE + 24
	24  WebKit                              0x0000000119274909 _ZN3IPC10Connection15dispatchMessageENSt3__110unique_ptrINS_7DecoderENS1_14default_deleteIS3_EEEE + 119
	25  WebKit                              0x000000011927717c _ZN3IPC10Connection18dispatchOneMessageEv + 176
	26  JavaScriptCore                      0x000000012232233d _ZN3WTF7RunLoop11performWorkEv + 333
	27  JavaScriptCore                      0x0000000122322552 _ZN3WTF7RunLoop11performWorkEPv + 34
	28  CoreFoundation                      0x0000000115b11101 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
	29  CoreFoundation                      0x0000000115bb0f71 __CFRunLoopDoSource0 + 81
	30  CoreFoundation                      0x0000000115af5a19 __CFRunLoopDoSources0 + 185
	31  CoreFoundation                      0x0000000115af4fff __CFRunLoopRun + 1279
	32  CoreFoundation                      0x0000000115af4889 CFRunLoopRunSpecific + 409
	33  EarlGrey                            0x0000000119166f4e -[GREYRunLoopSpinner grey_drainRunLoopInActiveModeAndCheckCondition:forTime:] + 590
	34  EarlGrey                            0x0000000119166968 -[GREYRunLoopSpinner spinWithStopConditionBlock:] + 424
	35  EarlGrey                            0x000000011916a17e -[GREYUIThreadExecutor executeSyncWithTimeout:block:error:] + 1006
	36  EarlGrey                            0x000000011913dfeb -[GREYElementInteraction assert:error:] + 1627
	37  EarlGrey                            0x000000011913f36b -[GREYElementInteraction assertWithMatcher:error:] + 123
	38  ios_chrome_ui_egtests               0x00000001087e0969 __42+[ChromeEarlGreyUI waitForToolbarVisible:]_block_invoke + 489
	39  ios_chrome_ui_egtests               0x0000000108788003 _ZN7testing27WaitUntilConditionOrTimeoutEdU13block_pointerFbvE + 115
	40  ios_chrome_ui_egtests               0x00000001087e041d +[ChromeEarlGreyUI waitForToolbarVisible:] + 1421
	41  ios_chrome_ui_egtests               0x000000010889f9cd -[FullscreenTestCase testChromeToChromeURLKeepsHeaderOnScreen] + 6173




*********************************************

-[FullscreenTestCase testHideHeaderUserScrollLongPage]
-[FullscreenTestCase testShowHeaderOnNativePageLoad]
-[FullscreenTestCase testShowHeaderOnReload]

[0509/195208.418467:FATAL:fullscreen_mediator.mm(182)] Check failed: (*animator).state == UIViewAnimatingStateActive (2 vs. 1)
0   ios_chrome_ui_egtests               0x0000000108c7ec7d base::debug::StackTrace::StackTrace(unsigned long) + 157
1   ios_chrome_ui_egtests               0x0000000108c7ecbd base::debug::StackTrace::StackTrace(unsigned long) + 29
2   ios_chrome_ui_egtests               0x000000010896f7ec base::debug::StackTrace::StackTrace() + 28
3   ios_chrome_ui_egtests               0x00000001089b58ac logging::LogMessage::~LogMessage() + 460
4   ios_chrome_ui_egtests               0x00000001089b3715 logging::LogMessage::~LogMessage() + 21
5   ios_chrome_ui_egtests               0x00000001075eea18 FullscreenMediator::StopAnimator(FullscreenAnimator* __strong*, bool) + 280
6   ios_chrome_ui_egtests               0x00000001075ed904 FullscreenMediator::StopAnimating(bool) + 516
7   ios_chrome_ui_egtests               0x00000001075ee1f7 FullscreenMediator::FullscreenModelWasReset(FullscreenModel*) + 39
8   ios_chrome_ui_egtests               0x00000001075f4925 FullscreenModel::ResetForNavigation() + 293
9   ios_chrome_ui_egtests               0x00000001075fb8ac FullscreenWebStateObserver::SetWebState(web::WebState*) + 140
10  ios_chrome_ui_egtests               0x00000001075fa667 FullscreenWebStateListObserver::WebStateActivatedAt(WebStateList*, web::WebState*, web::WebState*, int, int) + 103
11  ios_chrome_ui_egtests               0x000000010746a9aa WebStateList::NotifyIfActiveWebStateChanged(web::WebState*, int) + 314
12  ios_chrome_ui_egtests               0x0000000107468432 WebStateList::ActivateWebStateAt(int) + 306
13  ios_chrome_ui_egtests               0x000000010746765a WebStateList::InsertWebState(int, std::__1::unique_ptr<web::WebState, std::__1::default_delete<web::WebState> >, int, WebStateOpener) + 3546
14  ios_chrome_ui_egtests               0x00000001084f7368 -[TabModel insertTabWithLoadParams:opener:openedByDOM:atIndex:inBackground:] + 1784
15  ios_chrome_ui_egtests               0x00000001085d4cba -[TabGridAdaptor dismissWithNewTabAnimationToModel:withURL:atIndex:transition:] + 410
16  ios_chrome_ui_egtests               0x00000001085d9126 -[TabGridCoordinator openNewTab:] + 1158
17  ios_chrome_ui_egtests               0x0000000107e5bdb9 chrome_test_util::OpenNewTab() + 105
18  ios_chrome_ui_egtests               0x00000001087e4ee3 -[ChromeTestCase setUp] + 131
19  ios_chrome_ui_egtests               0x000000010889cfd3 -[FullscreenTestCase setUp] + 51