Add ClientCertStoreChromeOS which only returns the certs for a given user.

net/ssl/client_cert_store.h

Index: net/ssl/client_cert_store.h
diff --git a/net/ssl/client_cert_store.h b/net/ssl/client_cert_store.h
index 394d774f6c3e280a1d4e2d193374a005867444be..fe050e5f0993b8cf17b309f4000130693df9ad24 100644
--- a/net/ssl/client_cert_store.h
+++ b/net/ssl/client_cert_store.h
@@ -23,7 +23,8 @@ class NET_EXPORT ClientCertStore {
   // Get client certs matching the |cert_request_info|. On completion, the
   // results will be stored in |selected_certs| and the |callback| will be run.
   // The |callback| may be called sychronously. The caller must ensure the
-  // |selected_certs| object remains alive until the callback has been run.
+  // ClientCertStore and the |selected_certs| object remain alive until the
+  // callback has been run.
   virtual void GetClientCerts(const SSLCertRequestInfo& cert_request_info,
                               CertificateList* selected_certs,
                               const base::Closure& callback) = 0;