Fix some compiler warnings (miscellaneous)
https://bugs.webkit.org/show_bug.cgi?id=80790

Patch by Rob Buis <rbuis@rim.com> on 2013-05-08
Reviewed by Philip Rogers.

Get rid of the following warning for BlackBerry:

BackingStoreClient.cpp:54:21: warning: unused parameter 'parentFrame' [-Wunused-parameter]

by using ASSERT_UNUSED instead of ASSERT.

* WebKitSupport/BackingStoreClient.cpp:
(BlackBerry::WebKit::BackingStoreClient::create):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149763 268f45cc-cd09-0410-ab3c-d52691b4dbfc