example/main.go: avoid using clashing/unpublished ocagent version

Because of clashes with unpublished versions of opencensus-proto
as per census-instrumentation/opencensus-proto#161

we can't update ocagent to use the view.Exporter code, because
the unpublished opencensus-proto is what provides support for
the grpc-gateway. Hence this commit checks in the previous version
of example/main.go until that release.

example/main.go

@@ -22,10 +22,6 @@ import (
 	"time"
 
 	"contrib.go.opencensus.io/exporter/ocagent"
-
-	"go.opencensus.io/stats"
-	"go.opencensus.io/stats/view"
-	"go.opencensus.io/tag"
 	"go.opencensus.io/trace"
 )
 
@@ -35,50 +31,14 @@ func main() {
 		log.Fatalf("Failed to create ocagent-exporter: %v", err)
 	}
 	trace.RegisterExporter(oce)
-	view.RegisterExporter(oce)
-
 	trace.ApplyConfig(trace.Config{
 		DefaultSampler: trace.AlwaysSample(),
 	})
 
-	// By setting the reporting period to 4s, the underlying view.Data that's
-	// generated will be submitted to the view.Exporter-s every 4s.
-	view.SetReportingPeriod(4 * time.Second)
-
-	// Some stats
-	keyClient, _ := tag.NewKey("client")
-	keyMethod, _ := tag.NewKey("method")
-
-	mLatencyMs := stats.Float64("latency", "The latency in milliseconds", "ms")
-	views := []*view.View{
-		&view.View{
-			Name:        "opdemo/latency",
-			Description: "The latency of each iteration",
-			Measure:     mLatencyMs,
-			Aggregation: view.Distribution(0, 10, 50, 100, 200, 400, 800, 1000, 1400, 2000, 5000, 10000),
-			TagKeys:     []tag.Key{keyClient, keyMethod},
-		},
-		&view.View{
-			Name:        "opdemo/process_counts",
-			Description: "The various counts",
-			Measure:     mLatencyMs,
-			Aggregation: view.Count(),
-			TagKeys:     []tag.Key{keyClient, keyMethod},
-		},
-	}
-
-	if err := view.Register(views...); err != nil {
-		log.Fatalf("Failed to register views for metrics: %v", err)
-	}
-
-	ctx, _ := tag.New(context.Background(), tag.Insert(keyMethod, "repl"), tag.Insert(keyClient, "cli"))
 	rng := rand.New(rand.NewSource(time.Now().UnixNano()))
 	for {
-		startTime := time.Now()
-		_, span := trace.StartSpan(ctx, "Foo")
-		time.Sleep(time.Duration(rng.Int63n(13000)) * time.Millisecond)
+		_, span := trace.StartSpan(context.Background(), "foo")
+		time.Sleep(time.Duration(rng.Int63n(1000)) * time.Millisecond)
 		span.End()
-		latencyMs := float64(time.Since(startTime) / time.Millisecond)
-		stats.Record(ctx, mLatencyMs.M(latencyMs))
 	}
 }