Use external constants to enable setting group policies

The chrome builders are not joined to a domain, so the
`IntegrationTest.LegacyUpdate3Web` test fails. This change allows for
the test to run as if it were joined to a domain, which allows the test
to succeed. In addition, with using external constants, the registry
is not a constraint anymore, and arbitrary group policies can be set.

Bug: 1325740
Change-Id: I27cf7fc740d14284edb44c888992761cb41bde82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3654538
Reviewed-by: Sorin Jianu <sorin@chromium.org>
Commit-Queue: S. Ganesh <ganesh@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1006065}

diff --git a/chrome/updater/external_constants_default.cc b/chrome/updater/external_constants_default.cc
index 2fa257f..428426f1 100644
--- a/chrome/updater/external_constants_default.cc
+++ b/chrome/updater/external_constants_default.cc

@@ -5,6 +5,7 @@
 #include "chrome/updater/external_constants_default.h"
 
 #include "base/memory/scoped_refptr.h"
+#include "base/values.h"
 #include "chrome/updater/constants.h"
 #include "chrome/updater/external_constants.h"
 #include "chrome/updater/updater_branding.h"
@@ -35,6 +36,8 @@
     return crx_file::VerifierFormat::CRX3_WITH_PUBLISHER_PROOF;
   }
 
+  base::Value::DictStorage GroupPolicies() const override { return {}; }
+
  private:
   ~DefaultExternalConstants() override = default;
 };