git-cl: Use scm.GIT.{Get,Set}BranchConfig and {Get,Set}BranchRef instead of git calls.

scm.GIT functions are tested, and using them makes it easier to mock
git calls on git-cl tests.

Bug: 1051631
Change-Id: If067aa3f71b7478cafd7985d3020dacc0c6a41c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2055464Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

scm.py

@@ -187,12 +187,18 @@ class GIT(object):
   @staticmethod
   def GetBranchRef(cwd):
     """Returns the full branch reference, e.g. 'refs/heads/master'."""
+    try:
       return GIT.Capture(['symbolic-ref', 'HEAD'], cwd=cwd)
+    except subprocess2.CalledProcessError:
+      return None
 
   @staticmethod
   def GetBranch(cwd):
     """Returns the short branch name, e.g. 'master'."""
-    return GIT.ShortBranchName(GIT.GetBranchRef(cwd))
+    branchref = GIT.GetBranchRef(cwd)
+    if branchref:
+      return GIT.ShortBranchName(branchref)
+    return None
 
   @staticmethod
   def GetRemoteBranches(cwd):

tests/scm_unittest.py

@@ -198,6 +198,20 @@ class RealGitTest(fake_repos.FakeReposTestBase):
     scm.GIT.SetBranchConfig(self.cwd, branch, 'merge')
     scm.GIT.SetBranchConfig(self.cwd, branch, 'remote')
 
+  def testGetBranchRef(self):
+    self.assertEqual('refs/heads/master', scm.GIT.GetBranchRef(self.cwd))
+    HEAD = scm.GIT.Capture(['rev-parse', 'HEAD'], cwd=self.cwd)
+    scm.GIT.Capture(['checkout', HEAD], cwd=self.cwd)
+    self.assertIsNone(scm.GIT.GetBranchRef(self.cwd))
+    scm.GIT.Capture(['checkout', 'master'], cwd=self.cwd)
+
+  def testGetBranch(self):
+    self.assertEqual('master', scm.GIT.GetBranch(self.cwd))
+    HEAD = scm.GIT.Capture(['rev-parse', 'HEAD'], cwd=self.cwd)
+    scm.GIT.Capture(['checkout', HEAD], cwd=self.cwd)
+    self.assertIsNone(scm.GIT.GetBranchRef(self.cwd))
+    scm.GIT.Capture(['checkout', 'master'], cwd=self.cwd)
+
 
 if __name__ == '__main__':
   if '-v' in sys.argv: