Split the browsertests of safe browsing & content settings policies

Moved the browsertests of safe browsing policies  and content settings policies and all related stuff from policy_browsertests to separate files.

Bug: 1002483
Change-Id: If7a659bb7256ef3593802bb12cc89735bd636cfe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1929225
Commit-Queue: Aya Elsayed <ayaelattar@google.com>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718577}

chrome/test/BUILD.gn

@@ -1062,6 +1062,7 @@ if (!is_android) {
       "../browser/policy/cloud/cloud_policy_test_utils.h",
       "../browser/policy/cloud/component_cloud_policy_browsertest.cc",
       "../browser/policy/cloud/device_management_service_browsertest.cc",
+      "../browser/policy/content_settings_policy_browsertest.cc",
       "../browser/policy/policy_browsertest.cc",
       "../browser/policy/policy_initialization_browsertest.cc",
       "../browser/policy/policy_network_browsertest.cc",
@@ -1069,6 +1070,7 @@ if (!is_android) {
       "../browser/policy/policy_startup_browsertest.cc",
       "../browser/policy/policy_test_utils.cc",
       "../browser/policy/policy_test_utils.h",
+      "../browser/policy/safe_browsing_policy_browsertest.cc",
       "../browser/policy/site_isolation_policy_browsertest.cc",
       "../browser/portal/portal_browsertest.cc",
       "../browser/predictors/loading_predictor_browsertest.cc",