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There are assumptions that the IPC message limit is 128MB
so ChannelMojo has to allow messages in upto the message size.
Such large messages happen when IDB reads/writes huge records.

BUG=464151
R=agl@chromium.org

Review URL: https://codereview.chromium.org/1029703002

Cr-Commit-Position: refs/heads/master@{#322072}