gyp: cache conditional ASTs for 3 CPU seconds (5%) gain. 
gyp: cache conditional ASTs for 3 CPU seconds (5%) gain. 

This is in the parallel part so net gain is somewhere between 
5/core_count% and 5%. In chromium on my computer I save roughly 
1.5 seconds in total runtime. 

BUG=chromium:362075
R=mark@chromium.org

Review URL: https://codereview.chromium.org/232773004/
Patch from Daniel Bratell <bratell@opera.com>!


git-svn-id: e7e1075985beda50ea81ac4472467b4f6e91fc78@1900 78cadc50-ecff-11dd-a971-7dbc132099af

luvit/gyp,svn2github/gyp,luvit/gyp,luvit/gyp,svn2github/kgyp,svn2github/gyp,luvit/gyp,svn2github/kgyp,pyokagan/gyp,pyokagan/gyp,svn2github/gyp,svn2github/kgyp,svn2github/kgyp,pyokagan/gyp,pyokagan/gyp,svn2github/kgyp,svn2github/gyp,pyokagan/gyp,svn2github/gyp