Store build targets in the soong metrics.

Bug: 194519312
Test: Added unit test and verified the soong metrics file generated.
Change-Id: I832da2501e0e8d3435d4f92642cf45ddccb7f2ea
diff --git a/ui/metrics/metrics_proto/metrics.proto b/ui/metrics/metrics_proto/metrics.proto
index ef42f54..ec8f36b 100644
--- a/ui/metrics/metrics_proto/metrics.proto
+++ b/ui/metrics/metrics_proto/metrics.proto
@@ -123,6 +123,10 @@
   // Whether build is occurring in a mixed build mode, where Bazel maintains the
   // definition and build of some modules in cooperation with Soong.
   optional bool bazel_mixed_build = 5;
+
+  // These are the targets soong passes to ninja, these targets include special
+  // targets such as droid as well as the regular build targets.
+  repeated string targets = 6;
 }
 
 message SystemResourceInfo {