Add default implementation of experimental methods

components/cronet/android/api/src/org/chromium/net/ExperimentalBidirectionalStream.java

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.net;
 
 /**
  * {@link BidirectionalStream} that exposes experimental features.
  * Created using {@link Builder}. Every instance of {@link BidirectionalStream} can be casted
  * to an instance of this class.
@@ skipping 10 matching lines @@
     public abstract static class Builder extends BidirectionalStream.Builder {
         /**
          * Associates the annotation object with this request. May add more than one.
          * Passed through to a {@link RequestFinishedInfo.Listener},
          * see {@link RequestFinishedInfo#getAnnotations}.
          *
          * @param annotation an object to pass on to the {@link RequestFinishedInfo.Listener} with a
          * {@link RequestFinishedInfo}.
          * @return the builder to facilitate chaining.
          */
-        public abstract Builder addRequestAnnotation(Object annotation);
+        public Builder addRequestAnnotation(Object annotation) {
+            return this;
+        }
 
         // To support method chaining, override superclass methods to return an
         // instance of this class instead of the parent.
 
         @Override
         public abstract Builder setHttpMethod(String method);
 
         @Override
         public abstract Builder addHeader(String header, String value);
 
         @Override
         public abstract Builder setPriority(int priority);
 
         @Override
         public abstract Builder delayRequestHeadersUntilFirstFlush(
                 boolean delayRequestHeadersUntilFirstFlush);
 
         @Override
         public abstract ExperimentalBidirectionalStream build();
     }
 }