Don't use std::mutex::try_lock to check if we own a mutex
https://bugs.webkit.org/show_bug.cgi?id=133421

Reviewed by Dan Bernstein.

According the C++ standard, calling try_lock on a mutex that's already owned by the current thread
is undefined behavior, so don't do that.

* Modules/webdatabase/DatabaseBackendBase.cpp:
(WebCore::guidToVersionMap):
(WebCore::updateGuidVersionMap):
(WebCore::guidToDatabaseMap):
(WebCore::guidForOriginAndName):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@169503 268f45cc-cd09-0410-ab3c-d52691b4dbfc