Add source column to chrome://policy showing the origins of policies.

These are the possible sources for a policy:
Cloud - Policy values received from the cloud.
Platform - Local configured policies.
Enterprise Default - Defaults for policies in enterprise environments
                     on Chrome OS. Can be overridden.
Enterprise Override - Policies enforced in enterprise environments on
                      Chrome OS. Can NOT be overridden.

The source of a policy is determined when it's first set. For cloud
policies, this would be the decoding of the protocol buffers.
Platform policies are usually set by loading platform-specific local
configurations like entries in the Windows registry.
Enterprise defaults are automatically set if the device is active in
an enterprise environment.
Enterprise override policies are set within the code to enforce
specific behaviors (like ash tray visibility). They cannot be
overridden.

BUG=506123
TBR=jam@chromium.org

Review URL: https://codereview.chromium.org/1304843004

Cr-Commit-Position: refs/heads/master@{#349654}


CrOS-Libchrome-Original-Commit: 92e7960f06c2ac2ec0113bb88df3d322f0eb97fe
17 files changed
tree: b57e5168a36563408b2b1316cfcd3ed9df17aa0b
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/