Update Windows It2Me to allow remote users to interact with elevated windows

This changes updates the existing It2Me host for windows to use a second
process It2Me process (with the uiaccess flag in its manifest) to allow
the remote user to interact with elevated windows on the desktop.

BUG=617185

Review-Url: https://codereview.chromium.org/2179353004
Cr-Commit-Position: refs/heads/master@{#416778}
11 files changed