Fix test/variables/commands/update_golden. 

Without this fix, 

cd test/variables/commands && ./update_golden && cd - && \ 
./gyptest.py test/variables/commands 

led to failing tests. Now it works.
TBR=scottmg

Review URL: https://codereview.chromium.org/16047006

git-svn-id: http://gyp.googlecode.com/svn/trunk@1639 78cadc50-ecff-11dd-a971-7dbc132099af
Revert r1637, it broke gyp for chromium (due to use_titlecase_in_grd_files in
build/common.gypi).

Also revert r1638 since it's no longer needed.

Add tests for default variables in gypi files, especially for _files variables,
especially if those are ints (which were broken in chromium) or empty (which
was addressed by r1638).

The golden files were updated by running

   cd test/variables/commands && ./update_golden && cd -

TBR=torne

Review URL: https://codereview.chromium.org/15972007

git-svn-id: http://gyp.googlecode.com/svn/trunk@1640 78cadc50-ecff-11dd-a971-7dbc132099af