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* Behaviors specific to Controller are in a dedicated test.
* Each operator on Observable gets its own test file.
* Simplify ReactiveRecorder.
  * Rename entered() and exited() to opened() and closed().
  * Only watch one Observable per ReactiveRecorder.
  * Add an unsubscribe() method to test that scopes close.
  * Improve documentation in reactive_java.md.
* Add equals() method to Both so assertions are more useful.
  * Also added a hashCode() method for completeness.
* Use ReactiveRecorder more heavily than ArrayLists.

Bug: None
Test: cast_base_junit_tests, cast_shell_junit_tests
Change-Id: I2edd4627abe18523eb34482c648f8c15ffbfd89e
Reviewed-on: https://chromium-review.googlesource.com/1161459Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Simeon Anfinrud <sanfin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580723}