Unreviewed build fix for Qt WK2 after r140258.
Use the size_t type instead of unsigned for the variable
which holds the position of the first null character in the
console message.

* WebKitTestRunner/InjectedBundle/InjectedBundlePage.cpp:
(WTR::InjectedBundlePage::willAddMessageToConsole):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@140268 268f45cc-cd09-0410-ab3c-d52691b4dbfc