Added the AutoEnrollmentClient and unit tests for it.

chrome/browser/policy/browser_policy_connector.h

Index: chrome/browser/policy/browser_policy_connector.h
diff --git a/chrome/browser/policy/browser_policy_connector.h b/chrome/browser/policy/browser_policy_connector.h
index 50d4462ff6751d1d0bcdeb4f4040395824be869f..70cfaacb271d406344bad2b15de0f0d7a5accaf8 100644
--- a/chrome/browser/policy/browser_policy_connector.h
+++ b/chrome/browser/policy/browser_policy_connector.h
@@ -86,6 +86,9 @@ class BrowserPolicyConnector : public content::NotificationObserver {
   // Locks the device to an enterprise domain.
   EnterpriseInstallAttributes::LockResult LockDevice(const std::string& user);
 
+  // Returns the device serial number, or an empty string if not available.
+  static std::string GetSerialNumber();
+
   // Returns the enterprise domain if device is managed.
   std::string GetEnterpriseDomain();