Add ASCIILiteral() on strings allocated enough to appear in Instruments https://bugs.webkit.org/show_bug.cgi?id=118937

Merge http://trac.webkit.org/changeset/152948

R=eseidel

Review URL: https://chromiumcodereview.appspot.com/19577013

git-svn-id: svn://svn.chromium.org/blink/trunk@154620 bbb929c8-8fbe-4397-9dbb-9b2b20218538