Add chrome test support target to GN build.

Instead of putting all the files in a bit test_support target, I made separate smaller test support targets for the various sub-projects (browser, common, etc.) and linked those in. This helps distribute the complexity.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/559543003

Cr-Commit-Position: refs/heads/master@{#294641}
16 files changed