Add an example of an annotation-based TEST_MAPPING.

This change should be reverted once we have real instances of this
pattern and no longer need the example.

This change causes libcore.java.lang.PackageTest to be run in pre- and
post-submit for all libcore/luni changes. It demonstrates three
things:

1. Introducing a new annotation-based category of test, @Example in
   this case.
2. Applying the category to a test.
3. Adding a TEST_MAPPING which runs tests from that category.

Note that PackageTest#testGetPackages does not run, because it in
expectations/knownfailures.txt. (This is not to be confused with
PackageTest#testGetPackage, which does run.)

Google-internal: In treehugger run for this change, navigating through
aosp-master -> aosp_cf_x86_phone-userdebug -> test status ->
suite/test-mapping-presubmit-retry_cloud-tf, there is the test-mapping
presubmit run for this change for this change:
http://sponge/3531116c-6f5d-46d3-bdae-089c3c37e104. Under x86
CtsLibcoreTestCases it shows the expected four tests from PackageTest,
excluding testGetPackages.

Test: atest --test-mapping libcore/luni
Test: treehugger (see above)
Bug: 130283485
Change-Id: I8a3e929af2caf7aa22dd720750f407685d97f7a7

0 files changed, 0 insertions, 0 deletions