Leak fixed

BUG=skia:

Review URL: https://codereview.chromium.org/639423002
Remove references to out/Debug/tests executable.

This target does not exists anymore, it was folded into out/Debug/dm.
You can't do `ninja -C out/Debug tests` either anymore.

BUG=None
TEST=None
R=mtklein@google.com

Review URL: https://codereview.chromium.org/638913005
Clarify what DM means in the README file.

It took me a while to figure out what this acronym meant. ;)
Googling for it lead me to gyp/dm.gyp.

BUG=None
TEST=None
R=mtklein@google.com

Review URL: https://codereview.chromium.org/638083003