Add tests for makefile_writer.py.

Many of the tests performed are comparison tests, where we call the
functions using dummy values and then compare to expectations (also
newly added).

Add a way to rebaseline the test for write_android_mk, which is likely
to change in the future.

BUG=skia:1975
R=epoger@google.com

Author: scroggo@google.com

Review URL: https://codereview.chromium.org/205383006

git-svn-id: http://skia.googlecode.com/svn/trunk@13957 2bbb7eff-a529-9590-31e7-b0007b416f81
11 files changed