Apply OwnPtr|PassOwnPtr to handle member variables and arguments in MIDIClient

As r170438 and r170576, WebViewImpl has used m_midiClientProxy unnecessarily in order to pass it to provideMIDITo().
To remove it, this cl changes the parameter type to OwnPtr|PassOwnPtr in MIDIClient and MIDIControler
classes.

BUG=N/A

Review URL: https://codereview.chromium.org/220333003

git-svn-id: svn://svn.chromium.org/blink/trunk@170746 bbb929c8-8fbe-4397-9dbb-9b2b20218538