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.

Change-Id: Ifbf056ebb66da17c9e60244561340b3e1ccd4232
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_;
 };