Upgrade to golang protobuf api v2

Major operations:
 * Fix the go_package entries to be consistent, as the new tool
   complains when it doesn't have a '/'.
 * Regenerate with the new protoc-gen-go tool.
 * github.com/golang/protobuf -> google.golang.org/protobuf
 * proto.[Un]MarshalText -> prototext.[Un]Marshal

Change-Id: Ie1147bd2457fafb66ba555461b3bf14f0561a25d
diff --git a/ui/metrics/upload_proto/upload.proto b/ui/metrics/upload_proto/upload.proto
index bcd0ab2..e621fd1 100644
--- a/ui/metrics/upload_proto/upload.proto
+++ b/ui/metrics/upload_proto/upload.proto
@@ -15,7 +15,7 @@
 syntax = "proto2";
 
 package soong_metrics_upload;
-option go_package = "soong_metrics_upload_proto";
+option go_package = "android/soong/ui/metrics/upload_proto";
 
 message Upload {
   // The timestamp in milliseconds that the build was created.