webkit_tests fails flakily on:

virtual/spinvalidation/paint/invalidation/compositing/opacity-between-absolute2.html
virtual/spinvalidation/paint/invalidation/compositing/opacity-between-absolute.html

Examples:

https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Linux%20Trusty%20%28dbg%29/builds/194/steps/webkit_tests/logs/stdio
https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Win7%20%28dbg%29/builds/8340/steps/webkit_tests/logs/stdio

The check that fails was introduced in:

https://codereview.chromium.org/2546013002

Example stack trace:

02:40:26.791 24880 worker/3 virtual/spinvalidation/paint/invalidation/compositing/opacity-between-absolute2.html crashed, (stderr lines):
02:40:26.791 24880   [1:1:1206/024026.053481:1909496809:FATAL:FindPropertiesNeedingUpdate.h(144)] Check failed: *m_originalProperties->effect() == *objectProperties->effect(). Property was updated without the layout object ("LayoutBlockFlow DIV class='fader'") needing a paint property update.
02:40:26.791 24880   #0 0x7fcc9d2ba1de base::debug::StackTrace::StackTrace()
02:40:26.791 24880   #1 0x7fcc9d32767f logging::LogMessage::~LogMessage()
02:40:26.791 24880   #2 0x7fcc9452e363 blink::FindObjectPropertiesNeedingUpdateScope::~FindObjectPropertiesNeedingUpdateScope()
02:40:26.791 24880   #3 0x7fcc9452a337 blink::PaintPropertyTreeBuilder::updatePropertiesForSelf()
02:40:26.791 24880   #4 0x7fcc94546b76 blink::PrePaintTreeWalk::walk()
02:40:26.791 24880   #5 0x7fcc94546c26 blink::PrePaintTreeWalk::walk()
02:40:26.791 24880   #6 0x7fcc94546c26 blink::PrePaintTreeWalk::walk()
02:40:26.791 24880   #7 0x7fcc94546c26 blink::PrePaintTreeWalk::walk()
02:40:26.791 24880   #8 0x7fcc94546c26 blink::PrePaintTreeWalk::walk()
02:40:26.791 24880   #9 0x7fcc94546c26 blink::PrePaintTreeWalk::walk()
02:40:26.791 24880   #10 0x7fcc945468a1 blink::PrePaintTreeWalk::walk()
02:40:26.791 24880   #11 0x7fcc94546759 blink::PrePaintTreeWalk::walk()
02:40:26.791 24880   #12 0x7fcc93c677a7 blink::FrameView::updatePaintProperties()
02:40:26.791 24880   #13 0x7fcc93c666db blink::FrameView::updateLifecyclePhasesInternal()
02:40:26.791 24880   #14 0x7fcc93c65f02 blink::FrameView::updateAllLifecyclePhases()
02:40:26.791 24880   #15 0x7fcc944691cb blink::PageAnimator::updateAllLifecyclePhases()
02:40:26.791 24880   #16 0x7fcc96abd1e5 blink::PageWidgetDelegate::updateAllLifecyclePhases()
02:40:26.791 24880   #17 0x7fcc96bc4134 blink::WebViewImpl::updateAllLifecyclePhases()
02:40:26.791 24880   #18 0x7fcc96bba541 blink::WebViewFrameWidget::updateAllLifecyclePhases()
02:40:26.791 24880   #19 0x000000a06760 content::BlinkTestRunner::TestFinished()
02:40:26.792 24880   #20 0x7fcc9658a20a test_runner::TestRunner::NotifyDone()
02:40:26.792 24880   #21 0x7fcc96587bb8 test_runner::TestRunnerBindings::NotifyDone()
02:40:26.792 24880   #22 0x7fcc96508e15 _ZN4base8internal13FunctorTraitsIMN11test_runner31AccessibilityControllerBindingsEFvvEvE6InvokeIPS3_JEEEvS5_OT_DpOT0_
02:40:26.792 24880   #23 0x7fcc96508d81 _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKMN11test_runner31AccessibilityControllerBindingsEFvvEJPS5_EEEvOT_DpOT0_
02:40:26.792 24880   #24 0x7fcc96599266 _ZN4base8internal7InvokerINS0_9BindStateIMN11test_runner18TestRunnerBindingsEFvvEJEEEFvPS4_EE7RunImplIRKS6_RKSt5tupleIJEEJEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEEOS8_
02:40:26.792 24880   #25 0x7fcc965991cc _ZN4base8internal7InvokerINS0_9BindStateIMN11test_runner18TestRunnerBindingsEFvvEJEEEFvPS4_EE3RunEPNS0_13BindStateBaseEOS8_
02:40:26.792 24880   #26 0x7fcc96508b16 base::internal::RunMixin<>::Run()
02:40:26.792 24880   #27 0x7fcc96599103 _ZN3gin8internal7InvokerINS0_13IndicesHolderIJLm0EEEEJPN11test_runner18TestRunnerBindingsEEE18DispatchToCallbackEN4base8CallbackIFvS6_ELNS8_8internal8CopyModeE1ELNSB_10RepeatModeE1EEE
02:40:26.792 24880   #28 0x7fcc96598fa9 gin::internal::Dispatcher<>::DispatchToCallback()
02:40:26.792 24880   #29 0x7fcc97f1adc6 v8::internal::FunctionCallbackArguments::Call()
02:40:26.792 24880   #30 0x7fcc97fe75f3 v8::internal::(anonymous namespace)::HandleApiCallHelper<>()
02:40:26.792 24880   #31 0x7fcc97fe6120 v8::internal::Builtin_Impl_HandleApiCall()
02:40:26.792 24880   #32 0x13935528426e <unknown>

pdr, can you please take a look?