ShadowRoot.selection should be ShadowRoot.getSelection()

ShadowRoot.selection should be ShadowRoot.getSelection()
https://bugs.webkit.org/show_bug.cgi?id=86598

Reviewed by Hajime Morita.

Source/WebCore:

In the latest spec, ShadowRoot.selection is changed to ShadowRoot.getSelection().
So update the implementation.

* dom/ShadowRoot.cpp:
* dom/ShadowRoot.h:
(ShadowRoot):
* dom/ShadowRoot.idl:

LayoutTests:

In the latest spec, ShadowRoot.selection is changed to ShadowRoot.getSelection().
So update the tests.

* editing/shadow/selection-of-orphan-shadowroot.html:
* editing/shadow/selection-of-shadowroot.html: Removed unnecessary code to
call ShadowRoot.selection by using ShadowRoot.getSelection(). Now ShadowRoot.getSelection()
can be called directly.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@117421 268f45cc-cd09-0410-ab3c-d52691b4dbfc