Send an initial status update notification on bind().

When the client calls bind(), this patch now sends an initial status
update so the client can react to the status update that could have
been sent before it called bind().

Bug: 27108108
TEST=`update_engine_client --follow` shows the initial status.

(cherry picked from commit 0e061aebc651e041b6d1d8a3a91834feb87e0d62)

Change-Id: I4a8bd7a69054ead5e1ac144127452b64351d8082
diff --git a/binder_service_android.h b/binder_service_android.h
index 3e256e0..0a82b82 100644
--- a/binder_service_android.h
+++ b/binder_service_android.h
@@ -76,6 +76,11 @@
   // List of currently bound callbacks.
   std::vector<android::sp<android::os::IUpdateEngineCallback>> callbacks_;
 
+  // Cached copy of the last status update sent. Used to send an initial
+  // notification when bind() is called from the client.
+  int last_status_{-1};
+  double last_progress_{0.0};
+
   ServiceDelegateAndroidInterface* service_delegate_;
 };