GYP variable v8_optimized_debug should be overridable by GYP_DEFINES

Review URL: https://codereview.chromium.org/25430003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226772 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226772