After adding CHECK(!ScriptForbiddenScope::isScriptForbidden()) inside ScriptPromiseProperty::resolve, a number of animation related layout tests fail due to the assert being triggered. This indicates that promises are being resolved inside a forbidden scope (which means script could potentially be executed inside a forbidden scope).

Stack trace from web-animations-api/animation-ready-promise.html:

STDERR: [1:1:0105/142031.404897:1223641017798:FATAL:ScriptPromiseProperty.h(108)] Check failed: !ScriptForbiddenScope::isScriptForbidden(). 
STDERR: #0 0x7f5920dda6be base::debug::StackTrace::StackTrace()
STDERR: #1 0x7f5920e47cbf logging::LogMessage::~LogMessage()
STDERR: #2 0x7f5917232970 blink::ScriptPromiseProperty<>::resolve<>()
STDERR: #3 0x7f5917230d74 blink::Animation::resolveOrRejectReadyAndFinishedPromises()
STDERR: #4 0x7f591723089f blink::Animation::PlayStateUpdateScope::~PlayStateUpdateScope()
STDERR: #5 0x7f591722c3de blink::Animation::preCommit()
STDERR: #6 0x7f59172cce03 blink::CompositorPendingAnimations::update()
STDERR: #7 0x7f59172d599d blink::DocumentAnimations::updateAnimations()
STDERR: #8 0x7f59181f58ef blink::PaintLayerCompositor::updateIfNeededRecursiveInternal()
STDERR: #9 0x7f59181f55c8 blink::PaintLayerCompositor::updateIfNeededRecursive()
STDERR: #10 0x7f5917acb07e blink::FrameView::updateLifecyclePhasesInternal()
STDERR: #11 0x7f5917acaa72 blink::FrameView::updateAllLifecyclePhases()
STDERR: #12 0x7f59183a692b blink::PageAnimator::updateAllLifecyclePhases()
STDERR: #13 0x7f591a4ad695 blink::PageWidgetDelegate::updateAllLifecyclePhases()
STDERR: #14 0x7f591a5bf9d4 blink::WebViewImpl::updateAllLifecyclePhases()
STDERR: #15 0x7f5919fc0585 test_runner::WebWidgetTestClient::AnimateNow()
STDERR: #16 0x7f5919f1d247 _ZN4base8internal13FunctorTraitsIMN11test_runner16MockColorChooserEFvvEvE6InvokeIRKNS_7WeakPtrIS3_EEJEEEvS5_OT_DpOT0_
STDERR: #17 0x7f5919fc0a4a _ZN4base8internal12InvokeHelperILb1EvE8MakeItSoIRKMN11test_runner19WebWidgetTestClientEFvvERKNS_7WeakPtrIS5_EEJEEEvOT_OT0_DpOT1_
STDERR: #18 0x7f5919fc09d2 _ZN4base8internal7InvokerINS0_9BindStateIMN11test_runner19WebWidgetTestClientEFvvEJNS_7WeakPtrIS4_EEEEEFvvEE7RunImplIRKS6_RKSt5tupleIJS8_EEJLm0EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE
STDERR: #19 0x7f5919fc091c _ZN4base8internal7InvokerINS0_9BindStateIMN11test_runner19WebWidgetTestClientEFvvEJNS_7WeakPtrIS4_EEEEEFvvEE3RunEPNS0_13BindStateBaseE
STDERR: #20 0x7f5920de04b1 _ZNO4base8internal8RunMixinINS_8CallbackIFvvELNS0_8CopyModeE0ELNS0_10RepeatModeE0EEEE3RunEv
STDERR: #21 0x7f5920ddfe82 base::debug::TaskAnnotator::RunTask()
STDERR: #22 0x7f591ae9c6ea blink::scheduler::TaskQueueManager::ProcessTaskFromWorkQueue()
STDERR: #23 0x7f591ae9a111 blink::scheduler::TaskQueueManager::DoWork()
STDERR: #24 0x7f591aea2bac _ZN4base8internal13FunctorTraitsIMN5blink9scheduler16TaskQueueManagerEFvNS_9TimeTicksEbEvE6InvokeIRKNS_7WeakPtrIS4_EEJRKS5_RKbEEEvS7_OT_DpOT0_
STDERR: #25 0x7f591aea2a84 _ZN4base8internal12InvokeHelperILb1EvE8MakeItSoIRKMN5blink9scheduler16TaskQueueManagerEFvNS_9TimeTicksEbERKNS_7WeakPtrIS6_EEJRKS7_RKbEEEvOT_OT0_DpOT1_
STDERR: #26 0x7f591aea29e4 _ZN4base8internal7InvokerINS0_9BindStateIMN5blink9scheduler16TaskQueueManagerEFvNS_9TimeTicksEbEJNS_7WeakPtrIS5_EES6_bEEEFvvEE7RunImplIRKS8_RKSt5tupleIJSA_S6_bEEJLm0ELm1ELm2EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE
STDERR: #27 0x7f591aea28bc _ZN4base8internal7InvokerINS0_9BindStateIMN5blink9scheduler16TaskQueueManagerEFvNS_9TimeTicksEbEJNS_7WeakPtrIS5_EES6_bEEEFvvEE3RunEPNS0_13BindStateBaseE
STDERR: #28 0x7f5920de04b1 _ZNO4base8internal8RunMixinINS_8CallbackIFvvELNS0_8CopyModeE0ELNS0_10RepeatModeE0EEEE3RunEv
STDERR: #29 0x7f5920ddfe82 base::debug::TaskAnnotator::RunTask()
STDERR: #30 0x7f5920e70dda base::MessageLoop::RunTask()
STDERR: #31 0x7f5920e71064 base::MessageLoop::DeferOrRunPendingTask()
STDERR: #32 0x7f5920e7134e base::MessageLoop::DoWork()
STDERR: #33 0x7f5920e88ae3 base::MessagePumpDefault::Run()
STDERR: #34 0x7f5920e7095a base::MessageLoop::RunHandler()
STDERR: #35 0x7f5920f1e1b2 base::RunLoop::Run()
STDERR: #36 0x7f5923c3d91c content::RendererMain()
STDERR: #37 0x7f592404b13e content::RunZygote()
STDERR: #38 0x7f592404b4f0 content::RunNamedProcessTypeMain()
STDERR: #39 0x7f592404d8eb content::ContentMainRunnerImpl::Run()
STDERR: #40 0x7f592404a7e2 content::ContentMain()
STDERR: #41 0x000000492761 main
STDERR: #42 0x7f5912d0bf45 __libc_start_main
STDERR: #43 0x000000492635 <unknown>