Turn DeprecatedStringData's copy constructor into a static method to appease MSVC /W3

Turn DeprecatedStringData's copy constructor into a static method to appease MSVC /W3

DeprecatedStringData now has no public copy constructor. The single
call to the old one has been replaced with a call to the new
DeprecatedStringData::createAndAdopt static method.

Reviewed by Darin.

All regression tests pass.

* platform/DeprecatedString.cpp:
(WebCore::DeprecatedStringData::createAndAdopt):
(WebCore::DeprecatedStringData::adopt):
(WebCore::DeprecatedString::detachIfInternal):
* platform/DeprecatedString.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@23878 268f45cc-cd09-0410-ab3c-d52691b4dbfc