Update JSCIdentifier pretty printer in Tools/gdb/webkit.py
https://bugs.webkit.org/show_bug.cgi?id=115808

Patch by Denis Nomiyama <d.nomiyama@samsung.com> on 2013-05-08
Reviewed by Darin Adler.

The pretty printer for the JSCIdentifier in Tools/gdb/webkit.py
was left outdated after r127191, when the m_string member was changed
from UString to String. This patch calls the right pretty printer for it.

* gdb/webkit.py:
(JSCIdentifierPrinter.to_string): Use WTFPrettyPrinter instead of
WTFImplPrettyPrinter.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149775 268f45cc-cd09-0410-ab3c-d52691b4dbfc