Revert of scm.GIT.IsValidRevision: Only return True if the given object is a commit

scm.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """SCM-specific utility classes."""
 
 import cStringIO
 import glob
 import logging
 import os
@@ skipping 473 matching lines @@
     # the string and return code 0. So strip one character to force 'git
     # rev-parse' to do a hash table look-up and returns 128 if the hash is not
     # present.
     lookup_rev = rev
     if re.match(r'^[0-9a-fA-F]{40}$', rev):
       lookup_rev = rev[:-1]
     try:
       sha = GIT.Capture(['rev-parse', lookup_rev], cwd=cwd).lower()
       if lookup_rev != rev:
         # Make sure we get the original 40 chars back.
-        if rev.lower() != sha:
-          return False
+        return rev.lower() == sha
       if sha_only:
-        if not sha.startswith(rev.lower()):
-          return False
+        return sha.startswith(rev.lower())
+      return True
     except subprocess2.CalledProcessError:
       return False
-    obj_type = GIT.Capture(['cat-file', '-t', rev], cwd=cwd).strip()
-    return obj_type == 'commit'
 
   @classmethod
   def AssertVersion(cls, min_version):
     """Asserts git's version is at least min_version."""
     if cls.current_version is None:
       current_version = cls.Capture(['--version'], '.')
       matched = re.search(r'version ([0-9\.]+)', current_version)
       cls.current_version = matched.group(1)
     current_version_list = map(only_int, cls.current_version.split('.'))
     for min_ver in map(int, min_version.split('.')):
@@ skipping 627 matching lines @@
         # revert, like for properties.
         if not os.path.isdir(cwd):
           # '.' was deleted. It's not worth continuing.
           return
         try:
           SVN.Capture(['revert', file_status[1]], cwd=cwd)
         except subprocess2.CalledProcessError:
           if not os.path.exists(file_path):
             continue
           raise