metrics: Add guest mode detection to metrics library and client

Change-Id: I2c27bd999330395ba3568820ea76198b202bd7f4

BUG=7203
TEST=Verify metrics_client -c and -g toggling consent and guest mode.

Review URL: http://codereview.chromium.org/3571009
5 files changed
tree: 6b042e2e261430ce1393be52f6d09bfc1d0828a8
  1. metrics/