Add support for default rules to instrumentation test runners

This allows removing boilerplate rules (mostly annotation processors)
from test classes.

Also cleanup the inheritance hierarchy for the test runners:
ChromeJunit4ClassRunner now inherits from ContentJunit4ClassRunner.

Change-Id: I6672f1430bfcf1a3f90c1146ef6d943df08416e0
Reviewed-on: https://chromium-review.googlesource.com/1030450
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Tobias Sargeant <tobiasjs@chromium.org>
Commit-Queue: Bernhard Bauer <bauerb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562450}
23 files changed