Create a dummy MetricsReporterStub class

This handles the update_engine_sideload target, and thus avoiding
the insertion of "#ifdef _UE_SIDELOAD" everywhere when we report the
metrics for android.

Bug: 30989466
Test: build pass on marlin
Change-Id: Ib00ab8476218df15768bdbae1a3510f8584aa7c7
diff --git a/update_attempter_android.cc b/update_attempter_android.cc
index dbddfe3..6d67000 100644
--- a/update_attempter_android.cc
+++ b/update_attempter_android.cc
@@ -34,7 +34,7 @@
 #include "update_engine/common/file_fetcher.h"
 #include "update_engine/common/utils.h"
 #include "update_engine/daemon_state_interface.h"
-#include "update_engine/metrics_reporter_android.h"
+#include "update_engine/metrics_reporter_interface.h"
 #include "update_engine/metrics_utils.h"
 #include "update_engine/network_selector.h"
 #include "update_engine/payload_consumer/download_action.h"
@@ -92,8 +92,8 @@
       boot_control_(boot_control),
       hardware_(hardware),
       processor_(new ActionProcessor()),
-      clock_(new Clock()),
-      metrics_reporter_(new MetricsReporterAndroid()) {
+      clock_(new Clock()) {
+  metrics_reporter_ = metrics::CreateMetricsReporter();
   network_selector_ = network::CreateNetworkSelector();
 }