Which uses gsutil to download objects from Google Storage based on SHA1 sums 

Continuation of: https://chromiumcodereview.appspot.com/12317103/ 
Rietveld didn't like a giant CL with all of gsutil (kept crashing on upload), 
The CL is being split into three parts 

Related: 
https://chromiumcodereview.appspot.com/12685010/ (gsutil/gslib) 
https://codereview.chromium.org/12685009/ (gsutil/) 

Review URL: https://chromiumcodereview.appspot.com/12633019

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@188841 0039d316-1c4b-4281-b951-d872f2087c98