PRESUBMIT: Enforce tracker prefix for all BUG entries

Changed function definition from private to public. This was needed to test the function and to maintain the consistency.

BUG=webrtc:8197
NOTRY=True
R=kjellander@webrtc.org

Review-Url: https://codereview.webrtc.org/3010153002 .
Cr-Commit-Position: refs/heads/master@{#19831}

presubmit_test_mocks.py

@@ -0,0 +1,50 @@
+# Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+#
+# Use of this source code is governed by a BSD-style license
+# that can be found in the LICENSE file in the root of the source
+# tree. An additional intellectual property rights grant can be found
+# in the file PATENTS.  All contributing project authors may
+# be found in the AUTHORS file in the root of the source tree.
+
+
+class MockInputApi(object):
+  """Mock class for the InputApi class.
+
+  This class can be used for unittests for presubmit by initializing the files
+  attribute as the list of changed files.
+  """
+
+  def __init__(self):
+    self.change = MockChange([])
+
+
+class MockOutputApi(object):
+  """Mock class for the OutputApi class.
+
+  An instance of this class can be passed to presubmit unittests for outputing
+  various types of results.
+  """
+
+  class PresubmitResult(object):
+    def __init__(self, message, items=None, long_text=''):
+      self.message = message
+      self.items = items
+      self.long_text = long_text
+
+    def __repr__(self):
+      return self.message
+
+  class PresubmitError(PresubmitResult):
+    def __init__(self, message, items=None, long_text=''):
+      MockOutputApi.PresubmitResult.__init__(self, message, items, long_text)
+      self.type = 'error'
+
+class MockChange(object):
+  """Mock class for Change class.
+
+  This class can be used in presubmit unittests to mock the query of the
+  current change.
+  """
+
+  def __init__(self, changed_files):
+    self._changed_files = changed_files