Web MIDI: newly attached device was not registered to listen

Web MIDI: newly attached device was not registered to listen

Newly added MIDI input ports were detected and enumerated correctly,
but was not registered to listen. As a result, incoming MIDI messages
are not received at all.

BUG=n/a
TEST=manual

Committed: https://crrev.com/817e5460e9b9419937e9e5fe7a0f8f0874087770
Cr-Commit-Position: refs/heads/master@{#318655}

[Takashi Toyoshima, 2015-02-27 17:00:58]

toyoshim@chromium.org changed reviewers:
+ yhirano@chromium.org

[Takashi Toyoshima, 2015-02-27 18:04:20]

ptal

[yhirano, 2015-03-02 05:41:21]

lgtm

[Takashi Toyoshima, 2015-03-02 06:07:26]

The CQ bit was checked by toyoshim@chromium.org

[commit-bot: I haz the power, 2015-03-02 06:08:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/960213006/1

[commit-bot: I haz the power, 2015-03-02 06:44:58]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-02 06:45:29]

Patchset 1 (id:??) landed as
https://crrev.com/817e5460e9b9419937e9e5fe7a0f8f0874087770
Cr-Commit-Position: refs/heads/master@{#318655}