fix target location of unittest in dartium.deps/DEPS

[sigmundch]

Many packages now live in github and are pulled via gyp. The Dart repo uses third_party/pkg for all the packages that we pull in that way, and pkg only for packages that live in the repo. We have modified the dartium.deps/DEPS file to pull in packages this way too, except for unittest.

Unittest is temporarily pull it into:

  src/dart/pkg/unittest/

instead of:

  src/dart/third_party/pkg/unittest/

This is because some layout tests in Dartium refer to the old location. Technically we should change these tests and the DEPS files together to point to the new location. However, we are currently in the middle of a roll of Dartium and, using a different location for unittest minimizes the disruption/work we had to do at this moment.

We should fix the location either as soon as we are done with the roll or create a branch of Dartium to include these fixes.

Here is a patch with the required changes to the tests: https://codereview.chromium.org/819903002/

Here is the CL that temporarily updates DEPS to use pkg/unittest instead of third_party/pkg/unittest: https://codereview.chromium.org/816453006

[sigmundch]

FYI - because of the new location, the ./tools/test.py script pick up unittest tests, which wouldn't be picked up if they were under third_party/pkg.

We added a skip in the pkg.status file to avoid running these tests in the Dartium bots. (see https://codereview.chromium.org/819913003).

Note, these tests are covered by the package bots instead.

[whesse]

I have added the DEPS hook that downloads unittest into the third_party/pkg location, because it is needed there by the .packages file and the test http server that uses .packages. It should do no harm, being in the /pkg location as well, because the make_links tool is removed, with the removal of package root. It should still be a todo to remove it from the old location, and fix the tests that use it from there.