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

Revert of scm.GIT.IsValidRevision: Only return True if the given object is a commit (https://codereview.chromium.org/329823002/)

Reason for revert:
Speculative revert to see if this is the cause of auto_roll_test.py to fail in build/ presubmit.

Original issue's description:
> scm.GIT.IsValidRevision: Only return True if the given object is a commit
> 
> BUG=383476
> 
> Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=276487

TBR=iannucci@chromium.org,maruel@chromium.org,borenet@google.com
NOTREECHECKS=true
NOTRY=true
BUG=383476

Review URL: https://codereview.chromium.org/329393002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@276493 0039d316-1c4b-4281-b951-d872f2087c98

scm.py

@@ -491,15 +491,12 @@ class GIT(object):
       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):

tests/scm_unittest.py

@@ -8,7 +8,6 @@
 import logging
 import os
 import sys
-import tempfile
 import unittest
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
@@ -142,17 +141,6 @@ class RealGitTest(fake_repos.FakeReposTestBase):
     self.assertTrue(scm.GIT.IsValidRevision(cwd=self.clone_dir, rev=first_rev))
     self.assertTrue(scm.GIT.IsValidRevision(cwd=self.clone_dir, rev='HEAD'))
 
-    # Verify that IsValidRevision returns False for non-commit objects.
-    tmp = tempfile.NamedTemporaryFile(delete=False)
-    try:
-      tmp.write('This is not a commit')
-      tmp.close()
-      hashval = scm.GIT.Capture(['hash-object', '-w', tmp.name],
-                                cwd=self.clone_dir)
-    finally:
-      os.remove(tmp.name)
-    self.assertFalse(scm.GIT.IsValidRevision(cwd=self.clone_dir, rev=hashval))
-
 
 class RealGitSvnTest(fake_repos.FakeReposTestBase):
   def setUp(self):