The web components issue has a nice repro.

Patch up at https://codereview.chromium.org/2456773002

 Issue 644602  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5

commit b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5
Author: dominicc <dominicc@chromium.org>
Date: Fri Oct 28 05:04:00 2016

Clear the custom element's reaction queue if upgrade fails.

This is step 7."Finally, ...".2 of
<https://html.spec.whatwg.org/#concept-upgrade-an-element>

BUG= 645335 

Review-Url: https://codereview.chromium.org/2456773002
Cr-Commit-Position: refs/heads/master@{#428288}

[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/LayoutTests/custom-elements/spec/define-element.html
[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/LayoutTests/custom-elements/spec/resources/custom-elements-helpers.js
[delete] https://crrev.com/16319599c7ea406d03fbb402f905ccdc472114bd/third_party/WebKit/LayoutTests/custom-elements/spec/state-failed-upgrade-expected.txt
[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/LayoutTests/custom-elements/spec/state-failed-upgrade.html
[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/Source/core/BUILD.gn
[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/Source/core/dom/custom/CustomElementDefinition.cpp
[add] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/Source/core/dom/custom/CustomElementDefinitionTest.cpp
[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/Source/core/dom/custom/CustomElementReactionQueue.cpp
[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/Source/core/dom/custom/CustomElementReactionQueue.h
[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/Source/core/dom/custom/CustomElementReactionQueueTest.cpp
[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/Source/core/dom/custom/CustomElementReactionStack.cpp
[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/Source/core/dom/custom/CustomElementReactionStack.h
[modify] https://crrev.com/b2bda38bd5c73eeaed5198d7440cf5ddffe3a9c5/third_party/WebKit/Source/core/dom/custom/CustomElementReactionTestHelpers.h