[chromium] DRT crashes in an Aura/Win build
https://bugs.webkit.org/show_bug.cgi?id=111394

Reviewed by Tony Chang.

When building (and running) with use_aura=1, we assume that
we're using the default theme engine, but DRT creates the
DRTWin theme engine and overwrites the default, leading to crashes
in basically every test from the mismatch.

This fix gets us down to at least "lots of crashes" :).

* DumpRenderTree/chromium/TestShellWin.cpp:
(platformInit):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144802 268f45cc-cd09-0410-ab3c-d52691b4dbfc