Initial implementation for sharing field trial state (win)

This plumbs the field trial state string from the gpu and renderer host
processes and puts it in shared memory, passes the shared memory handle
(and length) via a command-line flag to the child, and the child will
initialize it there.

BUG=131632

Review-Url: https://codereview.chromium.org/2365273004
Cr-Commit-Position: refs/heads/master@{#425013}
19 files changed