Spinoff from http://crrev.com/2702483002 for  http://crbug.com/692310 . The tests execute and pass with a release build. Running locally with debug content shell however reports a fatal exception, sample below.

It reads as if somehow the main/worker thread property trees are in an incompatible/unexpected state.

This is likely the case for many or potentially all of the tests whose timeout failure is fixed in the above change.

% ./out/Default/content_shell --enable-slimming-paint-v2 --run-layout-test --expose-internals-for-testing --enable-threaded-compositing third_party/WebKit/LayoutTests/virtual/threaded/animations/KeyframeEffectReadOnly-composited-animation.html

#READY
Content-Type: text/plain
This is a testharness.js-based test.
PASS Using KeyframeEffect or KeyframeEffectReadOnly should not change whether an animation is composited 
Harness: the test ran to completion.

#EOF
#EOF
[1:5:0215/163108.596958:444071241420:FATAL:property_tree.h(68)] Check failed: i < static_cast<int>(nodes_.size()). 
#0 0x7f5bcfee829b base::debug::StackTrace::StackTrace()
#1 0x7f5bcfee68dc base::debug::StackTrace::StackTrace()
#2 0x7f5bcff51baf logging::LogMessage::~LogMessage()
#3 0x7f5bcbd1102b cc::PropertyTree<>::Node()
#4 0x7f5bcbfe66d7 cc::PropertyTrees::PushChangeTrackingTo()
#5 0x7f5bcbf8ee1b cc::LayerTreeHostImpl::ActivateSyncTree()
#6 0x7f5bcc0287a8 cc::ProxyImpl::ScheduledActionActivateSyncTree()
#7 0x7f5bcbeb8110 cc::Scheduler::ProcessScheduledActions()
#8 0x7f5bcbeb87c8 cc::Scheduler::NotifyReadyToActivate()
#9 0x7f5bcc025251 cc::ProxyImpl::NotifyReadyToActivate()
#10 0x7f5bcbf8a31a cc::LayerTreeHostImpl::NotifyReadyToActivate()
#11 0x7f5bcbf29fa8 cc::TileManager::CheckAndIssueSignals()
#12 0x7f5bcbd78d05 _ZN4base8internal13FunctorTraitsIMN2cc19CompositorFrameSinkEFvvEvE6InvokeIPS3_JEEEvS5_OT_DpOT0_
#13 0x7f5bcbf3b3f1 _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKMN2cc11TileManagerEFvvEJPS5_EEEvOT_DpOT0_
#14 0x7f5bcbf3b397 _ZN4base8internal7InvokerINS0_9BindStateIMN2cc11TileManagerEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE7RunImplIRKS6_RKSt5tupleIJS8_EEJLm0EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE
#15 0x7f5bcbf3b2dc _ZN4base8internal7InvokerINS0_9BindStateIMN2cc11TileManagerEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE3RunEPNS0_13BindStateBaseE
#16 0x7f5bcbcf33cb base::internal::RunMixin<>::Run()
#17 0x7f5bcc06b583 cc::UniqueNotifier::Notify()
#18 0x7f5bcbcf3057 _ZN4base8internal13FunctorTraitsIMN2cc28ScrollbarAnimationControllerEFvvEvE6InvokeIRKNS_7WeakPtrIS3_EEJEEEvS5_OT_DpOT0_
#19 0x7f5bcc06b7ca _ZN4base8internal12InvokeHelperILb1EvE8MakeItSoIRKMN2cc14UniqueNotifierEFvvERKNS_7WeakPtrIS5_EEJEEEvOT_OT0_DpOT1_
#20 0x7f5bcc06b752 _ZN4base8internal7InvokerINS0_9BindStateIMN2cc14UniqueNotifierEFvvEJNS_7WeakPtrIS4_EEEEEFvvEE7RunImplIRKS6_RKSt5tupleIJS8_EEJLm0EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE
#21 0x7f5bcc06b69c _ZN4base8internal7InvokerINS0_9BindStateIMN2cc14UniqueNotifierEFvvEJNS_7WeakPtrIS4_EEEEEFvvEE3RunEPNS0_13BindStateBaseE
#22 0x7f5bcfeee261 _ZNO4base8internal8RunMixinINS_8CallbackIFvvELNS0_8CopyModeE0ELNS0_10RepeatModeE0EEEE3RunEv
#23 0x7f5bcfeedade base::debug::TaskAnnotator::RunTask()
#24 0x7f5bcff7ad1d base::MessageLoop::RunTask()
#25 0x7f5bcff7afb4 base::MessageLoop::DeferOrRunPendingTask()
#26 0x7f5bcff7b2a4 base::MessageLoop::DoWork()
#27 0x7f5bcff92988 base::MessagePumpDefault::Run()
#28 0x7f5bcff7a8b7 base::MessageLoop::RunHandler()
#29 0x7f5bd0029b9a base::RunLoop::Run()
#30 0x7f5bd00d1664 base::Thread::Run()
#31 0x7f5bd00d1eca base::Thread::ThreadMain()
#32 0x7f5bd00b879a base::(anonymous namespace)::ThreadFunc()
#33 0x7f5bd5580184 start_thread
#34 0x7f5bc1e3e37d clone

Received signal 6
#0 0x7f5bcfee829b base::debug::StackTrace::StackTrace()
#1 0x7f5bcfee68dc base::debug::StackTrace::StackTrace()
#2 0x7f5bcfee7daf base::debug::(anonymous namespace)::StackDumpSignalHandler()
#3 0x7f5bd5588330 <unknown>
#4 0x7f5bc1d7ac37 gsignal
#5 0x7f5bc1d7e028 abort
#6 0x7f5bcfee4656 base::debug::(anonymous namespace)::DebugBreak()
#7 0x7f5bcfee4638 base::debug::BreakDebugger()
#8 0x7f5bcff51f46 logging::LogMessage::~LogMessage()
#9 0x7f5bcbd1102b #EOF
cc::PropertyTree<>::Node()
#10 0x7f5bcbfe66d7 cc::PropertyTrees::PushChangeTrackingTo()
#11 0x7f5bcbf8ee1b cc::LayerTreeHostImpl::ActivateSyncTree()
#12 0x7f5bcc0287a8 cc::ProxyImpl::ScheduledActionActivateSyncTree()
#13 0x7f5bcbeb8110 cc::Scheduler::ProcessScheduledActions()
#14 0x7f5bcbeb87c8 cc::Scheduler::NotifyReadyToActivate()
#15 0x7f5bcc025251 cc::ProxyImpl::NotifyReadyToActivate()
#16 0x7f5bcbf8a31a cc::LayerTreeHostImpl::NotifyReadyToActivate()
#17 0x7f5bcbf29fa8 cc::TileManager::CheckAndIssueSignals()
#18 0x7f5bcbd78d05 _ZN4base8internal13FunctorTraitsIMN2cc19CompositorFrameSinkEFvvEvE6InvokeIPS3_JEEEvS5_OT_DpOT0_
#19 0x7f5bcbf3b3f1 _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKMN2cc11TileManagerEFvvEJPS5_EEEvOT_DpOT0_
#20 0x7f5bcbf3b397 _ZN4base8internal7InvokerINS0_9BindStateIMN2cc11TileManagerEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE7RunImplIRKS6_RKSt5tupleIJS8_EEJLm0EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE
#21 0x7f5bcbf3b2dc _ZN4base8internal7InvokerINS0_9BindStateIMN2cc11TileManagerEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE3RunEPNS0_13BindStateBaseE
#22 0x7f5bcbcf33cb base::internal::RunMixin<>::Run()
#23 0x7f5bcc06b583 cc::UniqueNotifier::Notify()
#24 0x7f5bcbcf3057 _ZN4base8internal13FunctorTraitsIMN2cc28ScrollbarAnimationControllerEFvvEvE6InvokeIRKNS_7WeakPtrIS3_EEJEEEvS5_OT_DpOT0_
#25 0x7f5bcc06b7ca _ZN4base8internal12InvokeHelperILb1EvE8MakeItSoIRKMN2cc14UniqueNotifierEFvvERKNS_7WeakPtrIS5_EEJEEEvOT_OT0_DpOT1_
#26 0x7f5bcc06b752 _ZN4base8internal7InvokerINS0_9BindStateIMN2cc14UniqueNotifierEFvvEJNS_7WeakPtrIS4_EEEEEFvvEE7RunImplIRKS6_RKSt5tupleIJS8_EEJLm0EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE
#27 0x7f5bcc06b69c _ZN4base8internal7InvokerINS0_9BindStateIMN2cc14UniqueNotifierEFvvEJNS_7WeakPtrIS4_EEEEEFvvEE3RunEPNS0_13BindStateBaseE
#28 0x7f5bcfeee261 _ZNO4base8internal8RunMixinINS_8CallbackIFvvELNS0_8CopyModeE0ELNS0_10RepeatModeE0EEEE3RunEv