Add ShadowRoot.idl which is enabled by newly introduced SHADOW_DOM flag.

Add ShadowRoot.idl which is enabled by newly introduced SHADOW_DOM flag.
https://bugs.webkit.org/show_bug.cgi?id=76353

Reviewed by Hajime Morita.

Add ShadowRoot.idl, which is enabled only on chromium port since this is
under development feature.
ShadowRoot.idl contains minimum API so that we can test it.
Other APIs should be added on other changes so that we can isolate issues.

Source/WebCore:

Test: fast/dom/shadow/shadow-root-js-api.html

* WebCore.gypi:
* bindings/generic/RuntimeEnabledFeatures.cpp:
* bindings/generic/RuntimeEnabledFeatures.h:
(WebCore::RuntimeEnabledFeatures::shadowDOMEnabled):
(WebCore::RuntimeEnabledFeatures::setShadowDOMEnabled):
* dom/ShadowRoot.h:
(WebCore::ShadowRoot::host):
* dom/ShadowRoot.idl: Added.
* testing/Internals.cpp:
(WebCore::Internals::ensureShadowRoot):
(WebCore::Internals::shadowRoot):
* testing/Internals.h:
* testing/Internals.idl:

Source/WebKit/chromium:

* features.gypi:
* public/WebRuntimeFeatures.h:
* src/WebRuntimeFeatures.cpp:
(WebKit::WebRuntimeFeatures::enableShadowDOM):
(WebKit::WebRuntimeFeatures::isShadowDOMEnabled):

Tools:

* DumpRenderTree/chromium/TestShell.cpp:
(TestShell::TestShell):

LayoutTests:

* fast/dom/shadow/shadow-root-js-api-expected.txt: Added.
* fast/dom/shadow/shadow-root-js-api.html: Added.
* platform/efl/Skipped:
* platform/gtk/Skipped:
* platform/mac/Skipped:
* platform/qt/Skipped:
* platform/win/Skipped:
* platform/wincairo/Skipped:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@105500 268f45cc-cd09-0410-ab3c-d52691b4dbfc