Refactor ChromeOSPolicy into policy and utilities

Building on the policy fragments that have been previously extracted
from ChromeOSPolicy, this extracts a few more pieces of logic and
replaces sections of ChromeOSPolicy with calls to the extracted
methods.

Bug: 66016687
Test: unit tests, manually triggered OTA updates

Change-Id: I3bc608065f8ab89982f71b8490ebd66ed2266aa3
diff --git a/update_engine.gyp b/update_engine.gyp
index f72ca14..8111100 100644
--- a/update_engine.gyp
+++ b/update_engine.gyp
@@ -274,8 +274,15 @@
         'update_manager/boxed_value.cc',
         'update_manager/chromeos_policy.cc',
         'update_manager/default_policy.cc',
+        'update_manager/enough_slots_ab_updates_policy_impl.cc',
+        'update_manager/enterprise_device_policy_impl.cc',
         'update_manager/evaluation_context.cc',
+        'update_manager/interactive_update_policy_impl.cc',
+        'update_manager/next_update_check_policy_impl.cc',
+        'update_manager/official_build_check_policy_impl.cc',
+        'update_manager/out_of_box_experience_policy_impl.cc',
         'update_manager/policy.cc',
+        'update_manager/policy_test_utils.cc',
         'update_manager/real_config_provider.cc',
         'update_manager/real_device_policy_provider.cc',
         'update_manager/real_random_provider.cc',