Add PRESUBMIT_test.py for the root directory.
Add PRESUBMIT_test.py for the root directory.

This file was copied from chromium, with the test for extension IDL files
removed.

BUG=None
TEST=The test itself passed.
R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/681703002

chinmaygarde/mojo,jianglu/mojo,afandria/mojo,collinjackson/mojo,collinjackson/mojo,afandria/mojo,afandria/mojo,chinmaygarde/mojo,jianglu/mojo,collinjackson/mojo,afandria/mojo,jianglu/mojo,chinmaygarde/mojo,collinjackson/mojo,afandria/mojo,chinmaygarde/mojo,collinjackson/mojo,chinmaygarde/mojo,collinjackson/mojo,collinjackson/mojo,afandria/mojo,jianglu/mojo,chinmaygarde/mojo,jianglu/mojo,afandria/mojo,chinmaygarde/mojo,afandria/mojo,jianglu/mojo,jianglu/mojo,collinjackson/mojo,chinmaygarde/mojo,chinmaygarde/mojo,collinjackson/mojo,jianglu/mojo