[vpython] Incorporate interpreter path/hash.

vpython/api/vpython/env.proto

Index: vpython/api/vpython/env.proto
diff --git a/vpython/api/vpython/env.proto b/vpython/api/vpython/env.proto
index e077030d7315181f45806afa6964a9503936ef78..5ad6c283a29e670a2a24acc940ba931d042123f3 100644
--- a/vpython/api/vpython/env.proto
+++ b/vpython/api/vpython/env.proto
@@ -15,7 +15,21 @@ message Environment {
   // A constructed VirtualEnv.
   vpython.Spec spec = 1;
 
+  // The resolved runtime parameters.
+  Runtime runtime = 2;
+
   // The PEP425 tags that were probed for this Python environment.
-  repeated vpython.Pep425Tag pep425_tag = 2;
+  repeated vpython.Pep425Tag pep425_tag = 3;
+}
+
+
+// Runtime is the set of resolved runtime parameters.
+message Runtime {
+  // The absolute path to the resolved interpreter.
+  string path = 1;
+  // The SHA256 hash of the resolved interpreter.
+  string hash = 2;
+  // The resolved Python interpreter version.
+  string version = 3;
 }