Add --no-history option to fetch and gclient for shallow clones.

gclient.py

Index: gclient.py
diff --git a/gclient.py b/gclient.py
index b60884a0c2742bd55b43f01ddc5e5380af216bff..6068cd06c62736a9279c9f11a1d66f143a58ad46 100755
--- a/gclient.py
+++ b/gclient.py
@@ -1811,6 +1811,9 @@ def CMDsync(parser, args):
   parser.add_option('--shallow', action='store_true',
                     help='GIT ONLY - Do a shallow clone into the cache dir. '
                          'Requires Git 1.9+')
+  parser.add_option('--no-history', action='store_true',

[wtc, 2014/08/03 04:12:49]

It is unfortunate that the use of '_' or '-' in option names for the "sync"
command is inconsistent.

+                    help='GIT ONLY - Reduces the size/time of the checkout at '
+                    'the cost of no history. Requires Git 1.9+')

[iannucci, 2014/08/02 21:22:15]

it may be beneficial to specify a very low amount of history (like 1000
commits). If you could time that, it may be a good compromise between no history
and full history, especially if people are interested in recently-changed files.

[Primiano Tucci (use gerrit), 2014/08/03 17:43:34]

This is in principle a very nice feature. In practice, however, I feel this
would bump up the complexity of this change and require some major refactoring.
Explanation: I can easily change the --depth of the main project, that's a 1
line change. However, I won't be able to do the same for the subprojects. In
order to do that I'd need to fetch DEPS for src/HEAD~1000, recurse its deps, and
get the sha's for the shallow file.

Even the approximated version (just take the last 1000 commits for WebKit,
regardless of following deps) is not trivial, because I'd have still to find a
way to get the the sha of pinned_sha~1000 to put in the shallow file.

As regards the size, I did some git analysis back in this thread on
chromium-dev: http://goo.gl/FFsCdP
A depth of 5000 commits (which at the main project peace is ~= 3 months) is 1 GB
bigger than the shallow one. 

In short: unless you feel beneficial having a relatively small number  ~500  of
history just for the main project (even if this would make the term "no history"
a small lie), I'd leave this as it is. Just 3 months of history adds up to an
extra gig, which is several minutes.
IMHO it would be nice having a configurable --depth option for gclient, but, as
I was saying above, I'm afraid this require definitely more than 20-30 lines :)

   parser.add_option('--ignore_locks', action='store_true',
                     help='GIT ONLY - Ignore cache locks.')
   (options, args) = parser.parse_args(args)