Add a Ping() method to the trace service to make it easier to detect if the service is up and runni…

trace/service/traceservice.proto

 syntax = "proto3";
 
 package traceservice;
 
 // TraceService stores trace information for both Gold and Perf.
 service TraceService {
 
   // Returns a list of traceids that don't have Params stored in the datastore.
   rpc MissingParams(MissingParamsRequest) returns (MissingParamsResponse) {}
 
   // Adds Params for a set of traceids.
-  rpc AddParams(AddParamsRequest) returns (EmptyResponse) {}
+  rpc AddParams(AddParamsRequest) returns (Empty) {}
 
   // Adds data for a set of traces for a particular commitid.
-  rpc Add(AddRequest) returns (EmptyResponse) {}
+  rpc Add(AddRequest) returns (Empty) {}
 
   // Removes data for a particular commitid.
-  rpc Remove(RemoveRequest) returns (EmptyResponse) {}
+  rpc Remove(RemoveRequest) returns (Empty) {}
 
   // List returns all the CommitIDs that exist in the given time range.
   rpc List(ListRequest) returns (ListResponse) {}
 
   // GetValues returns all the trace values stored for the given CommitID.
   rpc GetValues(GetValuesRequest) returns (GetValuesResponse) {}
 
   // GetParams returns the Params for all of the given traces.
   rpc GetParams(GetParamsRequest) returns (GetParamsResponse) {}
+
+  // Ping should always succeed. Used to test if the service is up and
+  // running.
+  rpc Ping (GetParamsRequest) returns (Empty) {}
 }
 
-message EmptyResponse {
+message Empty {
 }
 
 // CommitID identifies one commit, or trybot try.
 message CommitID {
   // The id of a commit, either a git hash, or a Reitveld patch id.
   string id = 1;
 
   // The source of the commit, either a git branch name, or a Reitveld issue id.
   string source = 2;
 
@@ skipping 67 matching lines @@
 message GetParamsRequest {
   // A list of traceids.
   repeated string traceids = 1;
 }
 
 message GetParamsResponse {
   // Maps traceids to their Params.
   map<string, Params> params = 3;
 }