Send real data to Stackdriver and create registerExporter method

Author: eduardoemery

packages/opencensus-core/src/trace/model/trace.ts

@@ -28,6 +28,10 @@ export class Trace extends TraceBaseModel {
         super()
        this.setId((uuid.v4().split('-').join('')));
     }
+
+    public get traceSpans() : Span[] {
+        return this.spans;
+    }
 
     public start() {
         super.start()     

packages/opencensus-core/src/trace/model/tracer.ts

@@ -35,10 +35,9 @@ export class Tracer {
     //TODO: temp solution 
     private endedTraces: Trace[] = [];
 
-    constructor(exporter:Exporter) {
+    constructor() {
         this._active = false;
         this.contextManager = cls.createNamespace();
-        this.exporter = exporter;
     }
 
     public get currentTrace(): Trace  {
@@ -120,6 +119,10 @@ export class Tracer {
         namespace.bindEmitter(emitter);
     }
 
+    public registerExporter(exporter:Exporter) {
+        this.exporter = exporter;
+    }
+
 }