[CHROMIUM] Suppress c4267 build warnings for Win64 tests
https://bugs.webkit.org/show_bug.cgi?id=109359

Reviewed by Abhishek Arya.

* DumpRenderTree/DumpRenderTree.gyp/DumpRenderTree.gyp:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142379 268f45cc-cd09-0410-ab3c-d52691b4dbfc