Helium: Initial proto and Syncable interface definition

blimp/net/helium/vector_clock.cc

Index: blimp/net/helium/vector_clock.cc
diff --git a/blimp/net/helium/vector_clock.cc b/blimp/net/helium/vector_clock.cc
index 6b13d28745bd93e1ddb8793b4097e0c275709e98..41fcf0fffcc5f6fdc122d95ced5ff4f57a9393a8 100644
--- a/blimp/net/helium/vector_clock.cc
+++ b/blimp/net/helium/vector_clock.cc
@@ -54,4 +54,18 @@ void VectorClock::IncrementLocal() {
   local_revision_++;
 }
 
+helium::VectorClock VectorClock::CreateProto() {
+  helium::VectorClock result;

[CJ, 2016/09/29 20:36:55]

Is helium::VectorClock the message? Hard to tell. I'd suggest if so, add
"Message" at the end of the VectorClock proto name to make this explicit. 

[scf, 2016/09/29 23:13:39]

I was following the convention of other proto files. They neither specify a
namespace of a suffix in the class name. Thoughts?

[CJ, 2016/09/29 23:44:00]

The file names leave off the "message" part, but the actual messages defined in
the proto file have "Message".
Example:
https://cs.chromium.org/chromium/src/blimp/common/proto/ime.proto?rcl=1475162...

[scf, 2016/09/30 17:26:23]

HeliumMessage sounds good?

[CJ, 2016/09/30 19:47:12]

Well, this is for a VectorClock message right? So it should be
VectorClockMessage.

[scf, 2016/09/30 22:13:23]

talked offline. Suffixing everything to contain Message.

+  result.set_local_revision(local_revision_);
+  result.set_remote_revision(remote_revision_);
+  return result;
+}
+
+VectorClock VectorClock::Invert() {
+  VectorClock result;
+  result.set_local_revision(remote_revision_);
+  result.set_remote_revision(local_revision_);
+  return result;
+}
+
 }  // namespace blimp