Split login test base browsertests

The browsertests of login test base and all the related tests are moved
from policy_browsertests to a separate file.

Bug: 1084166
Change-Id: I63c270c7866d64ece3e3397e8914e31fc2b2872a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2207217
Commit-Queue: Swapnil Gupta <swapnilgupta@google.com>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770713}

chrome/test/BUILD.gn

@@ -1518,6 +1518,7 @@ if (!is_android) {
         "../browser/policy/accessibility_policy_browsertest.cc",
         "../browser/policy/arc_policy_browsertest.cc",
         "../browser/policy/assistant_policy_browsertest.cc",
+        "../browser/policy/login_policy_test_base_browsertest.cc",
         "../browser/policy/system_features_policy_browsertest.cc",
         "../browser/renderer_context_menu/quick_answers_menu_observer_browsertest.cc",
       ]