https://bugs.webkit.org/show_bug.cgi?id=77936

Reviewed by Hajime Morita.

Source/WebCore:

a video element and an audio element add UserAgentShadowRoot dynamically, and they assume that it's the oldest ShadowRoot.
However an AuthorShadowRoot could be added by a user before a video element and an audio element add UserAgentShadowRoot.
It breaks the assumption that the UserAgentShadowRoot is the oldest.

If the UserAgentShadowRoot is not the oldest, the AuthorShadowRoot a page author added might be ignored.
Since the timing to add UserAgentShadowRoot is not known by a user, the fact that UserAgentShadorRoot is
not the oldest will cause inconsistent behavior.

Adding AuthorShadowRoot to a video element and an audio element is allowed by this patch.

Test: fast/dom/shadow/shadowdom-for-media.html

* dom/ShadowRoot.cpp:
(WebCore::allowsAuthorShadowRoot):
* html/HTMLMediaElement.cpp:
(WebCore::HTMLMediaElement::createShadowSubtree):
(WebCore):
(WebCore::HTMLMediaElement::willAddAuthorShadowRoot):
(WebCore::HTMLMediaElement::createMediaControls):
* html/HTMLMediaElement.h:
(HTMLMediaElement):

LayoutTests:

Adding Shadow DOM to a video element and an audio element is allowed now.

* fast/dom/shadow/shadow-disable-expected.txt:
* fast/dom/shadow/shadow-disable.html:
* fast/dom/shadow/shadowdom-for-media-expected.txt: Added.
* fast/dom/shadow/shadowdom-for-media.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@122816 268f45cc-cd09-0410-ab3c-d52691b4dbfc