Web Audio: fix two bugs in audibility detection in BaseAudioContext.

Fixing the following issues:
 - take into account AudioContext stopping;
 - removes 10 seconds limitation.

TBR=mlamouri@chromium.org

(cherry picked from commit 1a0371469a2941c5d37464900be4404ceae55215)

Bug: 897451
Change-Id: I63b22fc20ded193cd032e30722ab35571adba56c
Reviewed-on: https://chromium-review.googlesource.com/c/1292378
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#601415}
Reviewed-on: https://chromium-review.googlesource.com/c/1297149
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/branch-heads/3538@{#1038}
Cr-Branched-From: 79f7c91a2b2a2932cd447fa6f865cb6662fa8fa6-refs/heads/master@{#587811}
1 file changed