[idle] Support Idle detection on Android.

We mocked out the android implementation in our early implementation, which
we address here. The AndroidIdleDetector makes bridge between the C++ idle
detection system and Android's Java Broadcast receivers.

Intent to implement:

https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/OuwzBmH02M4

Design doc:

https://docs.google.com/document/d/1_XlwY3NuG2HwWEYVrR-MNvw_i4hj5ZNj3gKvxWqO0FU/edit

Bug: 878979
Change-Id: I2a6c288c750574f1d777115d9e574c66a3dcbbdb
Reviewed-on: https://chromium-review.googlesource.com/c/1415296
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Sam Goto <goto@chromium.org>
Auto-Submit: Sam Goto <goto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632355}
6 files changed