Merge 276987 "Web MIDI: MidiManager crashes if a session is ende..."

Merge 276987 "Web MIDI: MidiManager crashes if a session is ende..."

> Web MIDI: MidiManager crashes if a session is ended while initializing
> 
> If a MidiManagerClient was destructed while an asynchronous MidiManager
> initialization performs, the browser process crashes when the
> initilization is finished. On EndSession(), MidiManager should remove
> the client even from |pending_clients_|.
> 
> Also, this change fixes a problem that CompleteStartSession() may not be
> invoked on a MidiManagerClient if its |client_id| is confclicting with
> another MidiManagerClient.
> 
> BUG=382522
> TEST=media_unittests --gtest_filter='Midi*'
> 
> Review URL: https://codereview.chromium.org/323323002

TBR=toyoshim@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=277617

[Takashi Toyoshima, 2014-06-17 02:05:02]

Committed patchset #1 manually as r277617.