The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6e97f9b878e58270e4a8d719800d16650c95459e

commit 6e97f9b878e58270e4a8d719800d16650c95459e
Author: hayato <hayato@chromium.org>
Date: Tue Mar 22 05:38:56 2016

Introduce DocumentOrShadowRoot Mixin

The spec is:
- https://dom.spec.whatwg.org/#documentorshadowroot
- http://w3c.github.io/webcomponents/spec/shadow/#extensions-to-the-documentorshadowroot-mixin

BUG= 595600 

Review URL: https://codereview.chromium.org/1815643002

Cr-Commit-Position: refs/heads/master@{#382515}

[modify] https://crrev.com/6e97f9b878e58270e4a8d719800d16650c95459e/third_party/WebKit/Source/core/core.gypi
[modify] https://crrev.com/6e97f9b878e58270e4a8d719800d16650c95459e/third_party/WebKit/Source/core/dom/Document.idl
[add] https://crrev.com/6e97f9b878e58270e4a8d719800d16650c95459e/third_party/WebKit/Source/core/dom/DocumentOrShadowRoot.h
[add] https://crrev.com/6e97f9b878e58270e4a8d719800d16650c95459e/third_party/WebKit/Source/core/dom/DocumentOrShadowRoot.idl
[modify] https://crrev.com/6e97f9b878e58270e4a8d719800d16650c95459e/third_party/WebKit/Source/core/dom/shadow/ShadowRoot.idl