cros: Add UMA metrics in encryption migration UI.
Some metrics about encryption migration are already recorded in cryptohomed.
In this CL, I'd like to add following UI-related UMA metrics on the app.
Cryptohome.MigrationUI.FirstScreen
Cryptohome.MigrationUI.UserChoice
Cryptohome.MigrationUI.ConsumedBatteryPercent
BUG=714887
TEST=Disable reboot after the migration by modifying the code, and check that chrome://histograms shows the added metrics.
Review-Url: https://codereview.chromium.org/2849833002
Cr-Commit-Position: refs/heads/master@{#468241}
3 files changed
