Initialize AtomicStringTable in WTFThreadData's constructor

Initialize AtomicStringTable in WTFThreadData's constructor
https://bugs.webkit.org/show_bug.cgi?id=117671

Reviewed by Geoffrey Garen.

Extracted AtomicStringTable from AtomicString.cpp into AtomicStringTable.h/cpp
and made WTFThreadDada::WTFThreadData create the atomic string table for the thread.

This eliminates a branch from stringTable() in AtomicString.cpp.

* GNUmakefile.list.am:
* WTF.pro:
* WTF.vcxproj/WTF.vcxproj:
* WTF.vcxproj/WTF.vcxproj.filters:
* WTF.xcodeproj/project.pbxproj:
* wtf/CMakeLists.txt:
* wtf/WTFThreadData.cpp:
(WTF::WTFThreadData::WTFThreadData):
* wtf/text/AtomicString.cpp:
(WTF::stringTable):
* wtf/text/AtomicStringTable.cpp: Added.
(WTF::AtomicStringTable::create):
(WTF::AtomicStringTable::destroy):
* wtf/text/AtomicStringTable.h: Added.
(WTF::AtomicStringTable::table):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@151663 268f45cc-cd09-0410-ab3c-d52691b4dbfc