Move type converter unittests to separate binary

Move type converter unittests to separate binary

There's no reason to lump the converter unit tests into
mojo_common_unittests as the converters are not under mojo/common. It is
also inconvenient to have the test targets in mojo/common as consumers
like flutter that want to use mojo/common do not necessarily want to
depend on converters they don't use. This moves the converter test
targets into their own binary, mojo_converters_unittests, and adds that
to the unittest list so mojob.py runs it.

R=viettrungluu@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/84ca926ffd1367cfa5213410d67bb7e66537388e

[jamesr, 2015-11-12 02:19:32]

jamesr@chromium.org changed reviewers:
+ viettrungluu@chromium.org

[viettrungluu, 2015-11-12 02:33:11]

lgtm

[jamesr, 2015-11-12 02:44:24]

Committed patchset #1 (id:1) manually as
84ca926ffd1367cfa5213410d67bb7e66537388e (presubmit successful).