cros: Add UMA metrics in encryption migration UI.

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}
(cherry picked from commit b75aa7267969141e12f5ece554be20d81d39b044)

Review-Url: https://codereview.chromium.org/2871493002 .
Cr-Commit-Position: refs/branch-heads/3071@{#444}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed: https://chromium.googlesource.com/chromium/src/+/3db95f093b5dd7c3924a74b577a60a3b12e1f968

[fukino, 2017-05-08 07:32:02]

Description was changed from

==========
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}
(cherry picked from commit b75aa7267969141e12f5ece554be20d81d39b044)
==========

to

==========
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}
(cherry picked from commit b75aa7267969141e12f5ece554be20d81d39b044)

Review-Url: https://codereview.chromium.org/2871493002 .
Cr-Commit-Position: refs/branch-heads/3071@{#444}
Cr-Branched-From:
a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed:
https://chromium.googlesource.com/chromium/src/+/3db95f093b5dd7c3924a74b577a6...
==========

[fukino, 2017-05-08 07:32:04]

Committed patchset #1 (id:1) manually as
3db95f093b5dd7c3924a74b577a60a3b12e1f968.