Return unicode commit hashes in checkout.GitCheckout.

The motivation for this CL is:
When a project is turned on to use GitCheckout with try job verifiers, then the CQ crashes because of line 64 in http://src.chromium.org/viewvc/chrome/trunk/tools/commit-queue/pending_manager.py

This is because revision can only be one of (None, int, unicode). This crash only happens when try jobs are used (which is why I did not see it before).
This CL changes the return type to be unicode instead of string.

Review URL: https://chromiumcodereview.appspot.com/25686005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@226743 0039d316-1c4b-4281-b951-d872f2087c98

checkout.py

@@ -622,8 +622,8 @@ class GitCheckout(CheckoutBase):
          '--quiet'])
 
   def _get_head_commit_hash(self):
-    """Gets the current revision from the local branch."""
-    return self._check_output_git(['rev-parse', 'HEAD']).strip()
+    """Gets the current revision (in unicode) from the local branch."""
+    return unicode(self._check_output_git(['rev-parse', 'HEAD']).strip())
 
   def apply_patch(self, patches, post_processors=None, verbose=False):
     """Applies a patch on 'working_branch' and switches to it.

tests/checkout_test.py

@@ -284,7 +284,9 @@ class SvnBaseTest(BaseTest):
       self.FAKE_REPOS.svn_dirty = True
 
     self.assertEquals(root, co.project_path)
-    self.assertEquals(self.previous_log['revision'], co.prepare(None))
+    svn_rev = co.prepare(None)
+    self.assertEquals(int, type(svn_rev))
+    self.assertEquals(self.previous_log['revision'], svn_rev)
     self.assertEquals('pouet', co.get_settings('bar'))
     self.assertTree(self.get_trunk(False), root)
     patches = self.get_patches()
@@ -377,7 +379,9 @@ class GitBaseTest(BaseTest):
       self.FAKE_REPOS.git_dirty = True
 
     self.assertEquals(root, co.project_path)
-    self.assertEquals(self.previous_log['revision'], co.prepare(None))
+    git_rev = co.prepare(None)
+    self.assertEquals(unicode, type(git_rev))
+    self.assertEquals(self.previous_log['revision'], git_rev)
     self.assertEquals('pouet', co.get_settings('bar'))
     self.assertTree(self.get_trunk(False), root)
     patches = self.get_patches()