Web MIDI: do not manage connection state from embedder side

Web MIDI: do not manage connection state from embedder side

In the latest spec, each MIDIPort has two separate states. One is
DeviceState, the other is ConnectionState. DeviceState represents the
device being "connected" or "disconnected". ConnectionState represents
the MIDIPort of each MIDIAccess actually being "open" the device or not.

ConnectionState is managed in Blink. So, content implementation do not
have to manage the state. In stead, it should manage actual MIDIAccess
client counts that open the device.

After this change,
 MIDI_PORT_DISCONNECTED: means the device is not connected to the system.
 MIDI_PORT_CONNECTED: means the device is connected to the system, but
     there are no actual clients that open the device.
 MIDI_PORT_OPEN: means the device is connected, and at least one client
     open the device.

BUG=471793
Committed: https://crrev.com/7f47161c5246973e5ed615221e938eab359edfc0
Cr-Commit-Position: refs/heads/master@{#323487}

[Takashi Toyoshima, 2015-04-02 09:31:16]

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

[Takashi Toyoshima, 2015-04-02 09:32:09]

Not urgent, but to remove MIDIPortConnectionState::ConnectionStateOpen in Blink
side.

[yhirano, 2015-04-02 11:46:26]

lgtm

[Takashi Toyoshima, 2015-04-02 13:44:22]

The CQ bit was checked by toyoshim@chromium.org

[commit-bot: I haz the power, 2015-04-02 13:44:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1054913002/20001

[commit-bot: I haz the power, 2015-04-02 15:08:59]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-03 20:25:29]

Patchset 2 (id:??) landed as
https://crrev.com/7f47161c5246973e5ed615221e938eab359edfc0
Cr-Commit-Position: refs/heads/master@{#323487}