Step two of optionally sending messages to/from message ports as base::Value.

Step two of optionally sending messages to/from message ports as base::Value.

This CL changes every place a MessagePort is transferred between process to
properly propagate the send_messages_as_values flag, as well as makes it
possible for NavigatorConnectContext to set this flag when setting up a
new connection.

This is part of a series of changes:
[1/5] Blink side changes in https://codereview.chromium.org/924983002/ that expose a needed v8 context
[2/5] https://codereview.chromium.org/921013002/ allow MessagePort to send messages as values
[3/5] This CL
[4/5] https://codereview.chromium.org/938403005/ which uses this for navigator.connect services and adds infrastructure for layout tests
[5/5] https://codereview.chromium.org/940423004/ adds layout tests to blink to test these new features

BUG=426458

Review URL: https://codereview.chromium.org/944443003

Cr-Commit-Position: refs/heads/master@{#318578}