Web MIDI: MIDI input messages may be lost or cause a crash on OS X

Web MIDI: MIDI input messages may be lost or cause a crash on OS X

MIDIPacketList can contain multiple MIDIPacket, but MIDIPacket objects
have different sizes depending on packet contents. So we should not
refer to MIDIPackets via array index, but should use MIDIPacketNext
that Core MIDI API provides to obtain the next object.

As a result, previous code may refer invalid memory region if large
MIDI messages are received at the same time.

BUG=456780, 374560
Committed: https://crrev.com/3cb91369e4dfa935884c0cdbfd1b664b0fe2c026
Cr-Commit-Position: refs/heads/master@{#318653}

[Takashi Toyoshima, 2015-02-27 15:47:37]

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

[Takashi Toyoshima, 2015-02-27 15:47:47]

ptal

[yhirano, 2015-03-02 05:35:42]

lgtm

[Takashi Toyoshima, 2015-03-02 06:06:24]

The CQ bit was checked by toyoshim@chromium.org

[commit-bot: I haz the power, 2015-03-02 06:07:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/965793002/1

[commit-bot: I haz the power, 2015-03-02 06:39:00]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-02 06:39:51]

Patchset 1 (id:??) landed as
https://crrev.com/3cb91369e4dfa935884c0cdbfd1b664b0fe2c026
Cr-Commit-Position: refs/heads/master@{#318653}