Split the browsertests of component updater policy

Moved the browsertests of component updater policy and all the related stuff out of policy_browsertest.cc & added TODO comment to refactor base::RunLoop::QuitCurrentWhenIdleDeprecated()

Bug: 1002483
Change-Id: Id92bc69cf4aea1ed015fb191bffed6cdafa12121
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1926138Reviewed-by: Sergey Poromov <poromov@chromium.org>
Commit-Queue: Aya Elsayed <ayaelattar@google.com>
Cr-Commit-Position: refs/heads/master@{#726408}

chrome/test/BUILD.gn

@@ -1079,6 +1079,7 @@ 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/component_updater_policy_browsertest.cc",
       "../browser/policy/content_settings_policy_browsertest.cc",
       "../browser/policy/policy_browsertest.cc",
       "../browser/policy/policy_initialization_browsertest.cc",