[WTF] Add the move constructor, move assignment operator for HashTable
https://bugs.webkit.org/show_bug.cgi?id=130772

Reviewed by Darin Adler.

HashTable has both copy constructor and copy assignment operator, meaning that the move constructor
and move assignment operator are implicitly deleted. This patch defines both to avoid unnecessary
copies when moves can be performed.

* wtf/HashTable.h:
(WTF::KeyTraits>::HashTable):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@170995 268f45cc-cd09-0410-ab3c-d52691b4dbfc