[android log] Add documentation and presubmit checks for log usage.

PRESUBMIT_test.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import glob
 import json
 import os
 import re
 import subprocess
@@ skipping 791 matching lines @@
 
     output = PRESUBMIT._CheckUserActionUpdate(input_api, MockOutputApi())
     self.assertEqual(
       ('File %s line %d: %s is missing in '
        'tools/metrics/actions/actions.xml. Please run '
        'tools/metrics/actions/extract_actions.py to update.'
        % (file_with_user_action, 1, 'NotInActionsXml')),
       output[0].message)
 
 
+class LogUsageTest(unittest.TestCase):
+
+  def testCheckNoNewUtilLogUsage(self):
+    mock_input_api = MockInputApi()
+    mock_output_api = MockOutputApi()
+
+    mock_input_api.files = [
+      MockAffectedFile('RandomStuff.java', [
+        'random stuff'
+      ]),
+      MockAffectedFile('HasCrLog.java', [
+        'import org.chromium.base.Log;',
+        'some random stuff',
+        'Log.d("TAG", "foo");',
+      ]),
+      MockAffectedFile('HasAndroidLog.java', [
+        'import android.util.Log;',
+        'some random stuff',
+        'Log.d("TAG", "foo");',
+      ]),
+      MockAffectedFile('HasExplicitLog.java', [
+        'some random stuff',
+        'android.util.Log.d("TAG", "foo");',
+      ]),
+      MockAffectedFile('HasBothLog.java', [
+        'import org.chromium.base.Log;',
+        'some random stuff',
+        'Log.d("TAG", "foo");',
+        'android.util.Log.d("TAG", "foo");',
+      ]),
+    ]
+
+    warnings = PRESUBMIT._CheckNoNewUtilLogUsage(
+        mock_input_api, mock_output_api)
+
+    self.assertEqual(1, len(warnings))
+    self.assertEqual(2, len(warnings[0].items))
+    self.assertTrue('HasAndroidLog.java' in warnings[0].items[0])
+    self.assertTrue('HasExplicitLog.java' in warnings[0].items[1])
+
+
 if __name__ == '__main__':
   unittest.main()