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

trace/service/traceservice_test.go

 package traceservice
 
 import (
         "encoding/binary"
         "fmt"
         "math"
         "os"
         "testing"
         "time"
 
@@ skipping 90 matching lines @@
                                         "config":   "gpu",
                                         "platform": "win8",
                                         "type":     "skp",
                                 },
                         },
                 },
         }
 
         ctx := context.Background()
 
+        // First confirm that Ping() works.
+        _, err = ts.Ping(ctx, &Empty{})
+        assert.Nil(t, err)
+
         // Confirm that these traceids don't have Params stored in the db yet.
         missingRequest := &MissingParamsRequest{
                 Traceids: []string{"key:8888:android", "key:gpu:win8"},
         }
         missingResp, err := ts.MissingParams(ctx, missingRequest)
         assert.NoError(t, err)
         assert.Equal(t, missingResp.Traceids, missingRequest.Traceids)
 
         // Now add the Params for them.
         _, err = ts.AddParams(ctx, params)
@@ skipping 104 matching lines @@
 
         b := c.ToBytes()
 
         // Test inputs that should fail.
         _, err = newCommitInfo(b[1:])
         assert.Error(t, err)
 
         _, err = newCommitInfo(b[:len(b)-1])
         assert.Error(t, err)
 }