Expose Add/RemoveActionCallback to java

Add support for testing user actions from Java by exposing
addActionCallback and removeActionCallback.
Add a UserActionTester class for java tests.
Add some tests for BrowsingDataBridge as an example.

There is already a similar approach for histogram tests using
getHistogramValueCountForTesting().

BUG=

Review-Url: https://codereview.chromium.org/2956283002
Cr-Commit-Position: refs/heads/master@{#485616}


CrOS-Libchrome-Original-Commit: 4f2ac33787e3661d3ce05d7aeb2429f300e08b82
3 files changed
tree: bf8c5c8bbd0aaba7e217cce2189aee8727e1a215
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/