https://build.chromium.org/p/chromium.fyi/builders/ios-simulator/builds/85/steps/ios_web_inttests%20%28iPhone%206s%20Plus%20iOS%209.0%29/logs/stdio

The crash stack below is not the actual error, that's just a timeout firing and CHECKing.  I think the actual errors are:

JavaScript error: SyntaxError: Unexpected token ')' URL:testwebui://testwebui/
JavaScript error: Error: Load timeout for modules: mojo/public/js/bindings,main


[----------] 1 test from WebUIMojoTest
[ RUN      ] WebUIMojoTest.MessageExchange
[INFO] GCDWebServer started on port 8080 and reachable at http://192.168.148.80:8080/
[INFO] GCDWebServer now reachable at http://build802-m4.local:8080/
[4813:1803:1215/174621.086651:4837009997990:ERROR:crw_web_controller.mm(3044)] JavaScript error: SyntaxError: Unexpected token ')' URL:testwebui://testwebui/
[4813:1803:1215/174629.081514:4845004679588:ERROR:crw_web_controller.mm(3044)] JavaScript error: Error: Load timeout for modules: mojo/public/js/bindings,main
http://requirejs.org/docs/errors.html#timeout URL:testwebui://testwebui/
[4813:1803:1215/174630.466389:4846389453002:FATAL:wait_util.mm(40)] Check failed: !condition || condition_evaluation_result.
0   ios_web_inttests                    0x0000000100bb2f0e _ZN4base5debug10StackTraceC2Ev + 30
1   ios_web_inttests                    0x0000000100bb2f75 _ZN4base5debug10StackTraceC1Ev + 21
2   ios_web_inttests                    0x0000000100c20160 _ZN7logging10LogMessageD2Ev + 80
3   ios_web_inttests                    0x0000000100c1de55 _ZN7logging10LogMessageD1Ev + 21
4   ios_web_inttests                    0x0000000100a3225f _ZN4base4test3ios18TimeUntilConditionEU13block_pointerFvvEU13block_pointerFbvEbNS_9TimeDeltaE + 751
5   ios_web_inttests                    0x0000000100a325a8 _ZN4base4test3ios18WaitUntilConditionEU13block_pointerFbvEbNS_9TimeDeltaE + 72
6   ios_web_inttests                    0x0000000100a32636 _ZN4base4test3ios18WaitUntilConditionEU13block_pointerFbvEPNS_11MessageLoopENS_9TimeDeltaE + 54
7   ios_web_inttests                    0x0000000100a325f1 _ZN4base4test3ios18WaitUntilConditionEU13block_pointerFbvE + 49
8   ios_web_inttests                    0x00000001006ab0f6 _ZN3web34WebUIMojoTest_MessageExchange_Test8TestBodyEv + 534
9   ios_web_inttests                    0x0000000100b71bae _ZN7testing8internal38HandleSehExceptionsInMethodIfSupportedINS_4TestEvEET0_PT_MS4_FS3_vEPKc + 126
10  ios_web_inttests                    0x0000000100b3f912 _ZN7testing8internal35HandleExceptionsInMethodIfSupportedINS_4TestEvEET0_PT_MS4_FS3_vEPKc + 114
11  ios_web_inttests                    0x0000000100b3f846 _ZN7testing4Test3RunEv + 198
12  ios_web_inttests                    0x0000000100b4187d _ZN7testing8TestInfo3RunEv + 221
13  ios_web_inttests                    0x0000000100b431fc _ZN7testing8TestCase3RunEv + 236
14  ios_web_inttests                    0x0000000100b58999 _ZN7testing8internal12UnitTestImpl11RunAllTestsEv + 873
15  ios_web_inttests                    0x0000000100b74a5e _ZN7testing8internal38HandleSehExceptionsInMethodIfSupportedINS0_12UnitTestImplEbEET0_PT_MS4_FS3_vEPKc + 126
16  ios_web_inttests                    0x0000000100b585b2 _ZN7testing8internal35HandleExceptionsInMethodIfSupportedINS0_12UnitTestImplEbEET0_PT_MS4_FS3_vEPKc + 114
17  ios_web_inttests                    0x0000000100b584a5 _ZN7testing8UnitTest3RunEv + 373
18  ios_web_inttests                    0x0000000100a33811 _Z13RUN_ALL_TESTSv + 17
19  ios_web_inttests                    0x0000000100a32d5a _ZN4base9TestSuite3RunEv + 330
20  ios_web_inttests                    0x0000000100a3682c -[ChromeUnitTestDelegate runTests] + 28
21  Foundation                          0x000000010636f129 __NSFireDelayedPerform + 402
22  CoreFoundation                      0x0000000105ae6364 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 20
23  CoreFoundation                      0x0000000105ae5f11 __CFRunLoopDoTimer + 1089
24  CoreFoundation                      0x0000000105aa78b1 __CFRunLoopRun + 1937
25  CoreFoundation                      0x0000000105aa6e98 CFRunLoopRunSpecific + 488
26  GraphicsServices                    0x0000000108cf1ad2 GSEventRunModal + 161
27  UIKit                               0x00000001045cc676 UIApplicationMain + 171
28  ios_web_inttests                    0x0000000100a36b72 _ZN4base18RunTestsFromIOSAppEv + 66
29  ios_web_inttests                    0x0000000100a32c2f _ZN4base9TestSuite3RunEv + 31
30  ios_web_inttests                    0x00000001006aab05 _ZN4base8internal13FunctorTraitsIMNS_9TestSuiteEFivEvE6InvokeIPN3web12WebTestSuiteEJEEEiS4_OT_DpOT0_ + 133
31  ios_web_inttests                    0x00000001006aaa24 _ZN4base8internal12InvokeHelperILb0EiE8MakeItSoIRKMNS_9TestSuiteEFivEJPN3web12WebTestSuiteEEEEiOT_DpOT0_ + 68
32  ios_web_inttests                    0x00000001006aa9cd _ZN4base8internal7InvokerINS0_9BindStateIMNS_9TestSuiteEFivEJNS0_17UnretainedWrapperIN3web12WebTestSuiteEEEEEEFivEE7RunImplIRKS5_RKNSt3__15tupleIJS9_EEEJLm0EEEEiOT_OT0_NS_13IndexSequenceIJXspT1_EEEE + 77
33  ios_web_inttests                    0x00000001006aa8ec _ZN4base8internal7InvokerINS0_9BindStateIMNS_9TestSuiteEFivEJNS0_17UnretainedWrapperIN3web12WebTestSuiteEEEEEEFivEE3RunEPNS0_13BindStateBaseE + 44
34  ios_web_inttests                    0x00000001015146db _ZNK4base8internal8RunMixinINS_8CallbackIFivELNS0_8CopyModeE1ELNS0_10RepeatModeE1EEEE3RunEv + 59
35  ios_web_inttests                    0x0000000100a38df4 _ZN4base15LaunchUnitTestsEiPPcRKNS_8CallbackIFivELNS_8internal8CopyModeE1ELNS4_10RepeatModeE1EEE + 996
36  ios_web_inttests                    0x00000001006aa668 main + 168
37  libdyld.dylib                       0x000000010b1f192d start + 1