https://bugs.webkit.org/show_bug.cgi?id=100575

Reviewed by Oliver Hunt.

Added StringImpl::create8BitIfPossible() that first tries to create an 8 bit string.  If it finds a 16 bit character
during processing, it calls the standard create() method.  The assumption is that this will be used on mostly 8 bit
strings and ones that are shorter (in the tens of characters).  Changed AtomicString to use the new creation method
for UChar based construction.

* wtf/text/AtomicString.cpp:
(WTF::UCharBufferTranslator::translate):
* wtf/text/StringImpl.cpp:
(WTF::StringImpl::create8BitIfPossible):
* wtf/text/StringImpl.h:
(WTF::StringImpl::create8BitIfPossible):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@132739 268f45cc-cd09-0410-ab3c-d52691b4dbfc