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..d5d9688178f5a72b529b81d921ef93834de4072e 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:
@@ -18,7 +20,7 @@ namespace blimp {
 // For more info see:
 // https://en.wikipedia.org/wiki/Vector_clock
 
-typedef uint32_t Revision;
+typedef uint64_t Revision;
 
 class VectorClock {
  public:
@@ -26,6 +28,7 @@ class VectorClock {
 
   VectorClock(Revision local_revision, Revision remote_revision);
   VectorClock();
+  VectorClock(const VectorClock&) = default;
 
   // Compares two vector clocks. There are 4 possibilities for the result:
   // * LessThan: One revision is equal and for the other is smaller.
@@ -56,6 +59,14 @@ class VectorClock {
     remote_revision_ = remote_revision;
   }
 
+  // Create the proto message corresponding to this object.
+  proto::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;