CL prepared:
https://chromium-review.googlesource.com/c/590367/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/715b9c42cf11b38a86a613be4ed195e49e8abfe8

commit 715b9c42cf11b38a86a613be4ed195e49e8abfe8
Author: Pavol Marko <pmarko@chromium.org>
Date: Wed Aug 30 18:30:57 2017

Introduce additional EcryptfsMigrationStrategy values

Introduce additional values for the EcryptfsMigrationStrategy policy:
- MinimalMigrate (value 4) in preparation for minimal migration mode.
  For now, this behaves as wipe (so if we merge only this back to M-61,
  the M-61 client will use "Wipe" when this policy comes in).
- AskForEcryptfsArcUsers (value 5) in preparation for the new default
  for EDU.

Additionally, this CL:
- Changes the default value (if the cached policy is too old to contain
  the value) to kDisallowMigration as per  crbug.com/747930 
- Fixes handling of max value in DecodeMigrationActionFromPolicy.

BUG= 747907 , 747930 

Change-Id: Ib800b7d34aade8507a2c8f853d224fb33df40b95
Reviewed-on: https://chromium-review.googlesource.com/641871
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Reviewed-by: Igor <igorcov@chromium.org>
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#498542}
[modify] https://crrev.com/715b9c42cf11b38a86a613be4ed195e49e8abfe8/chrome/browser/chromeos/arc/policy/arc_policy_util.h
[modify] https://crrev.com/715b9c42cf11b38a86a613be4ed195e49e8abfe8/chrome/browser/chromeos/login/existing_user_controller.cc
[modify] https://crrev.com/715b9c42cf11b38a86a613be4ed195e49e8abfe8/components/policy/resources/policy_templates.json

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a83b253ba61617231915dc02628dfead3eefcbb4

commit a83b253ba61617231915dc02628dfead3eefcbb4
Author: Pavol Marko <pmarko@chromium.org>
Date: Tue Sep 05 10:44:13 2017

[Merge to M61] Introduce additional EcryptfsMigrationStrategy values

Introduce additional values for the EcryptfsMigrationStrategy policy:
- MinimalMigrate (value 4) in preparation for minimal migration mode.
  For now, this behaves as wipe (so if we merge only this back to M-61,
  the M-61 client will use "Wipe" when this policy comes in).
- AskForEcryptfsArcUsers (value 5) in preparation for the new default
  for EDU.

Additionally, this CL:
- Changes the default value (if the cached policy is too old to contain
  the value) to kDisallowMigration as per  crbug.com/747930 
- Fixes handling of max value in DecodeMigrationActionFromPolicy.

BUG= 747907 , 747930 
TBR=pmarko@chromium.org

(cherry picked from commit 715b9c42cf11b38a86a613be4ed195e49e8abfe8)

Change-Id: Ib800b7d34aade8507a2c8f853d224fb33df40b95
Reviewed-on: https://chromium-review.googlesource.com/641871
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Reviewed-by: Igor <igorcov@chromium.org>
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#498542}
Reviewed-on: https://chromium-review.googlesource.com/649695
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Cr-Commit-Position: refs/branch-heads/3163@{#1098}
Cr-Branched-From: ff259bab28b35d242e10186cd63af7ed404fae0d-refs/heads/master@{#488528}
[modify] https://crrev.com/a83b253ba61617231915dc02628dfead3eefcbb4/chrome/browser/chromeos/arc/policy/arc_policy_util.h
[modify] https://crrev.com/a83b253ba61617231915dc02628dfead3eefcbb4/chrome/browser/chromeos/login/existing_user_controller.cc
[modify] https://crrev.com/a83b253ba61617231915dc02628dfead3eefcbb4/components/policy/resources/policy_templates.json

Note: the following summary only applies to managed users. Unmanaged users can always choose if they want to migrate.
Default value for not retrievable user policy or if the EcryptfsMigrationStrategy user policy value is missing are:
M61: 0 (DisallowMigration)
M62: GAIA user: 0 (DisallowMigration)
     AD user: 3 (AskUser)