GitLab

Uses a separate discovery session for LE scan requested by ARC.
Avoids triggering the DiscoveryStateChanged event for LE scan since
Android doesn't use it for LE scan. Note that We still use a timer for
LE scan since we cannot set scan parameters and filters now, while
this is not expected by Android.

BUG=b:145257789
BUG=b:152463320
TEST=Automatic cts tests passed;
TEST=Manually test with the app mentioned in the bug thread, the
behavior becomes normal.

Change-Id: I9b9d24827896678b24592260eefd48e7aa2b89c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2010606Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Miao-chen Chou <mcchou@chromium.org>
Commit-Queue: Jie Jiang <jiejiang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760371}