Expose signing key from cloud policy stores

chrome/browser/chromeos/policy/device_local_account_policy_store.cc

Index: chrome/browser/chromeos/policy/device_local_account_policy_store.cc
diff --git a/chrome/browser/chromeos/policy/device_local_account_policy_store.cc b/chrome/browser/chromeos/policy/device_local_account_policy_store.cc
index ab474719445c5a6235b07478cd85d2e39446f6c0..a2ed9bc3dfe11c1420cf14d31991b6f9d2cc436c 100644
--- a/chrome/browser/chromeos/policy/device_local_account_policy_store.cc
+++ b/chrome/browser/chromeos/policy/device_local_account_policy_store.cc
@@ -149,6 +149,7 @@ void DeviceLocalAccountPolicyStore::Validate(
     NotifyStoreLoaded();
     return;
   }
+  public_key_ = key->as_string();
 
   std::unique_ptr<UserCloudPolicyValidator> validator(
       UserCloudPolicyValidator::Create(std::move(policy_response),
@@ -177,10 +178,8 @@ void DeviceLocalAccountPolicyStore::Validate(
   validator->ValidatePayload();
   policy::BrowserPolicyConnectorChromeOS* connector =
       g_browser_process->platform_part()->browser_policy_connector_chromeos();
-  validator->ValidateSignature(key->as_string(),
-                               GetPolicyVerificationKey(),
-                               connector->GetEnterpriseDomain(),
-                               false);
+  validator->ValidateSignature(public_key_, GetPolicyVerificationKey(),
+                               connector->GetEnterpriseDomain(), false);
   validator.release()->StartValidation(callback);
 }