Reland 'media: Add "Hide players" button in about://media-internals' with fix

Reland 'media: Add "Hide players" button in about://media-internals' with fix

This relands 4ee2eeb27fb5cb49b1d5fa470528c16738d0274d with fix.

Original CL description:

What this does is:
- Adds a button to hide all current players on the page, but doesn't
  touch the C++ side to actually delete those players.
- After a player is hidden, new logs for that player will be dropped
  and will not resurrect any hidden players.
- If a user refreshes the media-internals page, or open a new one,
  we'll get all players back.

Fix:

In manager.js, handle the case where the button may not exist, e.g. in
tests.

TBR=sandersd@chromium.org
BUG=688607
Review-Url: https://codereview.chromium.org/2682803004
Cr-Commit-Position: refs/heads/master@{#449087}
Committed: https://chromium.googlesource.com/chromium/src/+/46844f6e8ad264cd4b20a3d75c0d3a8c303333bb

[xhwang, 2017-02-08 20:43:20]

The CQ bit was checked by xhwang@chromium.org

[commit-bot: I haz the power, 2017-02-08 20:43:57]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-02-08 20:56:49]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1486586600388770,
"parent_rev": "0fa9bae07ce76f127ec4d254ed1ff9879f9b26e0", "commit_rev":
"46844f6e8ad264cd4b20a3d75c0d3a8c303333bb"}

[commit-bot: I haz the power, 2017-02-08 20:57:29]

Description was changed from

==========
Reland 'media: Add "Hide players" button in about://media-internals' with fix

This relands 4ee2eeb27fb5cb49b1d5fa470528c16738d0274d with fix.

Original CL description:

What this does is:
- Adds a button to hide all current players on the page, but doesn't
  touch the C++ side to actually delete those players.
- After a player is hidden, new logs for that player will be dropped
  and will not resurrect any hidden players.
- If a user refreshes the media-internals page, or open a new one,
  we'll get all players back.

Fix:

In manager.js, handle the case where the button may not exist, e.g. in
tests.

TBR=sandersd@chromium.org
BUG=688607
==========

to

==========
Reland 'media: Add "Hide players" button in about://media-internals' with fix

This relands 4ee2eeb27fb5cb49b1d5fa470528c16738d0274d with fix.

Original CL description:

What this does is:
- Adds a button to hide all current players on the page, but doesn't
  touch the C++ side to actually delete those players.
- After a player is hidden, new logs for that player will be dropped
  and will not resurrect any hidden players.
- If a user refreshes the media-internals page, or open a new one,
  we'll get all players back.

Fix:

In manager.js, handle the case where the button may not exist, e.g. in
tests.

TBR=sandersd@chromium.org
BUG=688607

Review-Url: https://codereview.chromium.org/2682803004
Cr-Commit-Position: refs/heads/master@{#449087}
Committed:
https://chromium.googlesource.com/chromium/src/+/46844f6e8ad264cd4b20a3d75c0d...
==========

[commit-bot: I haz the power, 2017-02-08 20:57:35]

Committed patchset #2 (id:20001) as
https://chromium.googlesource.com/chromium/src/+/46844f6e8ad264cd4b20a3d75c0d...