Fix for undesired audio blip when closing a muted tab.

Fix for undesired audio blip when closing a muted tab.

AudioRendererHost was calling AudioMirroringManager::RemoveDiverter()
just before AudioOutputController::Close().  This caused AOC to re-start
the default audio output stream (to the user's speakers) for 0-50+
milliseconds before closing and shutting down.  This change fixes the
problem by moving the RemoveDiverter() call to a point after AOC has
completed its close operation, which results in no new streams starting
up during this shutdown process.

BUG=474432
Committed: https://crrev.com/04eb0d223d2aaa440839ac7d9fe47148fcae83ac
Cr-Commit-Position: refs/heads/master@{#333684}

[miu, 2015-06-10 00:34:43]

miu@chromium.org changed reviewers:
+ dalecurtis@google.com

[miu, 2015-06-10 00:34:44]

dalecurtis: PTAL.

[DaleCurtis, 2015-06-10 00:38:26]

dalecurtis@chromium.org changed reviewers:
+ dalecurtis@chromium.org

[DaleCurtis, 2015-06-10 00:38:26]

lgtm

[miu, 2015-06-10 03:28:55]

The CQ bit was checked by miu@chromium.org

[miu, 2015-06-10 03:28:55]

The patchset sent to the CQ was uploaded after l-g-t-m from
dalecurtis@chromium.org
Link to the patchset: https://codereview.chromium.org/1172883003/#ps20001
(title: "Fix crash on Windows (grab pointer before scoped_ptr is passed).")

[commit-bot: I haz the power, 2015-06-10 03:29:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1172883003/20001

[commit-bot: I haz the power, 2015-06-10 04:30:03]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-06-10 04:31:51]

Patchset 2 (id:??) landed as
https://crrev.com/04eb0d223d2aaa440839ac7d9fe47148fcae83ac
Cr-Commit-Position: refs/heads/master@{#333684}