Don't launch sub-process through shell.
Don't launch sub-process through shell.

Setting shell=True causes CygWin to open a Python
interactive prompt rather than download/copy file.
Since there are no actual shell meta-characters in
the command, there shouldn't be any problems in
forking the command directly.

BUG=

Review URL: https://codereview.chromium.org/1231863014

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#339086}

Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Just-D/chromium-1,Just-D/chromium-1,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Just-D/chromium-1,Chilledheart/chromium,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Just-D/chromium-1,Just-D/chromium-1,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Just-D/chromium-1,axinging/chromium-crosswalk,Just-D/chromium-1,Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Just-D/chromium-1,axinging/chromium-crosswalk,Chilledheart/chromium,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Just-D/chromium-1,axinging/chromium-crosswalk