Enable magic window mode with new Gvr

Magic window mode was disabled(not reporting phone sensor
data) here: https://codereview.chromium.org/2367673002/
The reason was new API requires an Activity instead of a
context like before. This CL moves the initialization of
GVR to chrome so CTA is available.

BUG=389343

Review-Url: https://codereview.chromium.org/2398103002
Cr-Commit-Position: refs/heads/master@{#425035}
13 files changed