Reapply r186598 with fix for 'gclient revert'.

gclient_scm.py

Index: gclient_scm.py
===================================================================
--- gclient_scm.py	(revision 186973)
+++ gclient_scm.py	(working copy)
@@ -655,6 +655,11 @@
       detach_head = True
     if options.verbose:
       clone_cmd.append('--verbose')
+    # Don't assume 'with_branch_heads' is added by 'gclient sync' setup, since
+    # _Clone() can by reached in roundabout ways (e.g. 'gclient revert').
+    if hasattr(options, 'with_branch_heads') and 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 +682,15 @@
       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 (hasattr(options, 'with_branch_heads') and
+            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.