Always load extension policies from the stable preference domain

All channels load Chrome policies from the stable bundle id domain. So
should the extension policies.

Bug: 1163895, 831577
Change-Id: Id5bc4d5fcb0bffdc9444a53328d1ec9d20cb9008
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2630230Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844339}

components/policy/core/common/policy_loader_mac.mm

@@ -188,7 +188,7 @@ base::FilePath PolicyLoaderMac::GetManagedPolicyPath(CFStringRef bundle_id) {
 void PolicyLoaderMac::LoadPolicyForDomain(PolicyDomain domain,
                                           const std::string& domain_name,
                                           PolicyBundle* bundle) {
-  std::string id_prefix(base::mac::BaseBundleID());
+  std::string id_prefix(base::SysCFStringRefToUTF8(application_id_));
   id_prefix.append(".").append(domain_name).append(".");
 
   const ComponentMap* components = schema_map()->GetComponents(domain);