Collect FORCE_USE_GOMA environment variable as a metric.

FORCE_USE_GOMA is needed to be collected as a metric for the
deprecation of GOMA on Android builds.

Bug: b/169423400
Test: m nothing, ran printproto command
Change-Id: I12300389f1f27239d8f21875d1b6e4ad069d95d7
diff --git a/ui/metrics/metrics_proto/metrics.proto b/ui/metrics/metrics_proto/metrics.proto
index 6559ba3..4d6118b 100644
--- a/ui/metrics/metrics_proto/metrics.proto
+++ b/ui/metrics/metrics_proto/metrics.proto
@@ -102,6 +102,8 @@
   optional bool use_goma = 1;
 
   optional bool use_rbe = 2;
+
+  optional bool force_use_goma = 3;
 }
 
 message PerfInfo {