Expose ast via InputApi

To be used by https://chromium-review.googlesource.com/c/593708/

Bug:
Change-Id: I0d005bf6a6ba4262197a222cb337308551ed61a6
Reviewed-on: https://chromium-review.googlesource.com/595308
Commit-Queue: Takeshi Yoshino <tyoshino@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>

presubmit_support.py

@@ -12,6 +12,7 @@ __version__ = '1.8.0'
 # caching (between all different invocations of presubmit scripts for a given
 # change). We should add it as our presubmit scripts start feeling slow.
 
+import ast  # Exposed through the API.
 import cpplint
 import cPickle  # Exposed through the API.
 import cStringIO  # Exposed through the API.
@@ -402,6 +403,7 @@ class InputApi(object):
 
     # We expose various modules and functions as attributes of the input_api
     # so that presubmit scripts don't have to import them.
+    self.ast = ast
     self.basename = os.path.basename
     self.cPickle = cPickle
     self.cpplint = cpplint

tests/presubmit_unittest.py

@@ -160,7 +160,7 @@ class PresubmitUnittest(PresubmitTestsBase):
       'GitChange', 'InputApi', 'ListRelevantPresubmitFiles', 'main',
       'NonexistantCannedCheckFilter', 'OutputApi', 'ParseFiles',
       'PresubmitFailure', 'PresubmitExecuter', 'PresubmitOutput', 'ScanSubDirs',
-      'auth', 'cPickle', 'cpplint', 'cStringIO', 'contextlib',
+      'ast', 'auth', 'cPickle', 'cpplint', 'cStringIO', 'contextlib',
       'canned_check_filter', 'fix_encoding', 'fnmatch', 'gclient_utils',
       'git_footers', 'glob', 'inspect', 'json', 'load_files', 'logging',
       'marshal', 'normpath', 'optparse', 'os', 'owners', 'owners_finder',
@@ -960,6 +960,7 @@ class InputApiUnittest(PresubmitTestsBase):
         'ReadFile',
         'RightHandSideLines',
         'ShutdownPool',
+        'ast',
         'basename',
         'cPickle',
         'cpplint',