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PLY yacc parse table creation is (obviously) expensive.
Pre-caching this in a separate build step substantially improves build time.

Improves build time (user time) by 45% on my Linux box:
1m 50s => 59s

BUG=341748
R=haraken

Review URL: https://codereview.chromium.org/184233005

git-svn-id: svn://svn.chromium.org/blink/trunk@168611 bbb929c8-8fbe-4397-9dbb-9b2b20218538