Helium: Initial proto and Syncable interface definition

blimp/net/helium/vector_clock.h

Index: blimp/net/helium/vector_clock.h
diff --git a/blimp/net/helium/vector_clock.h b/blimp/net/helium/vector_clock.h
index c375aacc274a52b642d5da580c22579180ef25db..17dbe247bd6b10d48282cb6a66d56f25a73b6c35 100644
--- a/blimp/net/helium/vector_clock.h
+++ b/blimp/net/helium/vector_clock.h
@@ -7,6 +7,8 @@
 
 #include <stdint.h>
 
+#include "blimp/common/proto/helium.pb.h"
+
 namespace blimp {
 
 // From wikipedia:
@@ -56,6 +58,14 @@ class VectorClock {
     remote_revision_ = remote_revision;
   }
 
+  // Create the proto message object corresponding to this object.
+  helium::VectorClockMessage ToProto() const;
+
+  // Inverts the local and remote components respectively
+  // Used when we send VectorClock across the wire. The local becomes
+  // remote and vice versa.
+  VectorClock Invert() const;
+
  private:
   Revision local_revision_ = 0;
   Revision remote_revision_ = 0;