Add USE(PLATFORM_STRATEGIES) ifdefs to StorageNamespace.cpp
https://bugs.webkit.org/show_bug.cgi?id=112004

Patch by Carlos Garcia Campos <cgarcia@igalia.com> on 2013-03-18
Reviewed by Rob Buis.

Check if platform strategies is enabled before using it, falling
back to StorageNamespaceImpl if it isn't.

* storage/StorageNamespace.cpp:
(WebCore::StorageNamespace::localStorageNamespace):
(WebCore::StorageNamespace::sessionStorageNamespace):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146065 268f45cc-cd09-0410-ab3c-d52691b4dbfc