To bring parity with travis build add missing tasks to kokoro build.
- Each task is treated as separate job to run in parallel.
- single script linux_presumbit.sh performs all task based TASK env.
diff --git a/scripts/check-git-history.py b/scripts/check-git-history.py
index 1aba2ca..df13e42 100644
--- a/scripts/check-git-history.py
+++ b/scripts/check-git-history.py
@@ -4,7 +4,8 @@
 
 def main(argv):
   # Only check the history if the build is running on a pull request.
-  if is_travis_pull_request():
+  # Build could be running on pull request using travis or kokoro.
+  if is_travis_pull_request() or is_kokoro_presubmit_request():
     # This function assumes that HEAD^1 is the base branch and HEAD^2 is the
     # pull request.
     exit_if_pull_request_has_merge_commits()
@@ -12,9 +13,17 @@
   else:
     print 'Skipped history check.'
 
+def is_kokoro_presubmit_request():
+  '''Returns true if KOKORO_GITHUB_PULL_REQUEST_NUMBER is set.'''
+  if 'KOKORO_GITHUB_PULL_REQUEST_NUMBER' in os.environ:
+    return True
+  return False
+
 def is_travis_pull_request():
   '''Returns true if TRAVIS_PULL_REQUEST is set to indicate a pull request.'''
-  return os.environ['TRAVIS_PULL_REQUEST'] != 'false'
+  if 'TRAVIS_PULL_REQUEST' in os.environ:
+    return os.environ['TRAVIS_PULL_REQUEST'] != 'false'
+  return False
 
 def exit_if_pull_request_has_merge_commits():
   '''Exits with an error if any of the commits added by the pull request are