Tell call/channel op handlers who is invoking them.

This change adds a parameter to all op handlers specifying the invoking filter.
It will be used to allow client_channel to distinguish which child channel is
disconnecting or going away.
	Change on 2014/12/10 by ctiller <ctiller@google.com>
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=81823231