Guarantee build_id is a string. (#1248)

Guarantee build_id is a string rather than occasionally an int when
fetched from commit count rather than commit message.

b/295907476

Change-Id: I4b4ab42b8984a8fd38c276329e62c08c0a94bc0e
(cherry picked from commit 12c750e)

cobalt/build/build_info.py

@@ -57,7 +57,7 @@ def get_build_id_from_commit_count(cwd):
   output = subprocess.check_output(['git', 'rev-list', '--count', 'HEAD'],
                                    cwd=cwd)
   build_id = int(output.strip().decode()) + COMMIT_COUNT_BUILD_ID_OFFSET
-  return build_id
+  return str(build_id)
 
 
 def _get_last_commit_with_format(placeholder, cwd):

cobalt/build/get_build_id_test.py

@@ -87,8 +87,9 @@ def testGetBuildNumberFromCommitCountSunnyDay(self):
       self.make_commit()
     build_number = build_info.get_build_id_from_commit_count(
         cwd=self.test_dir.name)
-    self.assertEqual(build_number,
-                     num_commits + build_info.COMMIT_COUNT_BUILD_ID_OFFSET)
+    self.assertEqual(
+        int(build_number),
+        num_commits + build_info.COMMIT_COUNT_BUILD_ID_OFFSET)
 
   def testCommitsOutrankCommitCount(self):
     self.make_commit()
@@ -102,8 +103,9 @@ def testFallbackToCommitCount(self):
     for _ in range(num_commits):
       self.make_commit()
     build_number = get_build_id.main(cwd=self.test_dir.name)
-    self.assertEqual(build_number,
-                     num_commits + build_info.COMMIT_COUNT_BUILD_ID_OFFSET)
+    self.assertEqual(
+        int(build_number),
+        num_commits + build_info.COMMIT_COUNT_BUILD_ID_OFFSET)
 
 
 if __name__ == '__main__':