Add option to automatically fetch git "branch-heads".

The "branch-heads" are refspecs created from upstream svn branches. This flag
is mostly needed for official builders, and adds about 1/2GB of data to the
checkout, so not currently enabling by default.
Review URL: https://codereview.chromium.org/12546017

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@186598 0039d316-1c4b-4281-b951-d872f2087c98

gclient.py

@@ -1476,6 +1476,10 @@ def CMDsync(parser, args):
                          'has multiple solutions configured and will work even '
                          'if the src@ part is skipped. Note that specifying '
                          '--revision means your safesync_url gets ignored.')
+  parser.add_option('--with_branch_heads', action='store_true',
+                    help='Clone git "branch_heads" refspecs in addition to '
+                         'the default refspecs. This adds about 1/2GB to a '
+                         'full checkout. (git only)')
   parser.add_option('-t', '--transitive', action='store_true',
                     help='When a revision is specified (in the DEPS file or '
                           'with the command-line flag), transitively update '

gclient_scm.py

@@ -655,6 +655,9 @@ class GitWrapper(SCMWrapper):
       detach_head = True
     if options.verbose:
       clone_cmd.append('--verbose')
+    if options.with_branch_heads:
+      clone_cmd.extend(['--config', 'remote.origin.fetch=+refs/branch-heads/*:'
+                        'refs/remotes/branch-heads/*'])
     clone_cmd.extend([url, self.checkout_path])
 
     # If the parent directory does not exist, Git clone on Windows will not
@@ -677,6 +680,14 @@ class GitWrapper(SCMWrapper):
       try:
         self._Run(clone_cmd, options, cwd=self._root_dir, filter_fn=_GitFilter,
                   print_stdout=False)
+        # Update the "branch-heads" remote-tracking branches, since clone
+        # doesn't automatically fetch those, and we might need it to checkout a
+        # specific revision below.
+        if options.with_branch_heads:
+          fetch_cmd = ['fetch', 'origin']
+          if options.verbose:
+            fetch_cmd.append('--verbose')
+          self._Run(fetch_cmd, options)
         break
       except subprocess2.CalledProcessError, e:
         # Too bad we don't have access to the actual output yet.