Milo: Add LogDog annotation stream support.

appengine/cmd/milo/logdog/stream.proto

Index: appengine/cmd/milo/logdog/stream.proto
diff --git a/appengine/cmd/milo/logdog/stream.proto b/appengine/cmd/milo/logdog/stream.proto
new file mode 100644
index 0000000000000000000000000000000000000000..d88b57ada71bf85c09a4ab251268dc0beee39ce7
--- /dev/null
+++ b/appengine/cmd/milo/logdog/stream.proto
@@ -0,0 +1,20 @@
+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+syntax = "proto3";
+
+package logdog;
+
+import "github.com/luci/luci-go/common/proto/milo/annotations.proto";
+
+/**

[nodir, 2016/07/29 18:42:06]

nit: I think we use // everywhere, in particular in milo

[dnj, 2016/07/29 19:57:35]

Done.

+ * Item is a full annotation protobuf state item.

[nodir, 2016/07/29 18:42:06]

please add a comment that this message is not intended to be used outside of
this package, and actually an implementation detail

[dnj, 2016/07/29 19:57:35]

Done.

+ */
+message Item {
+  /** Step is the root annotation step. */
+  milo.Step step = 1;
+
+  /** Finished is true if this is the last annotation protobuf in the stream. */
+  bool finished = 2;
+}