fix: rename response observer and callbacks (#1291)

Rename HeaderTracer* to BigtableTracer*

Author: mutianf

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/metrics/BigtableTracerStreamingCallable.java

@@ -58,22 +58,22 @@ public void call(
  final GrpcResponseMetadata responseMetadata = new GrpcResponseMetadata();
  // tracer should always be an instance of bigtable tracer
  if (context.getTracer() instanceof BigtableTracer) {
- HeaderTracerResponseObserver<ResponseT> innerObserver =
- new HeaderTracerResponseObserver<>(
+ BigtableTracerResponseObserver<ResponseT> innerObserver =
+ new BigtableTracerResponseObserver<>(
  responseObserver, (BigtableTracer) context.getTracer(), responseMetadata);
  innerCallable.call(request, innerObserver, responseMetadata.addHandlers(context));
  } else {
  innerCallable.call(request, responseObserver, context);
  }
  }
 
- private class HeaderTracerResponseObserver<ResponseT> implements ResponseObserver<ResponseT> {
+ private class BigtableTracerResponseObserver<ResponseT> implements ResponseObserver<ResponseT> {
 
  private final BigtableTracer tracer;
  private final ResponseObserver<ResponseT> outerObserver;
  private final GrpcResponseMetadata responseMetadata;
 
- HeaderTracerResponseObserver(
+ BigtableTracerResponseObserver(
  ResponseObserver<ResponseT> observer,
  BigtableTracer tracer,
  GrpcResponseMetadata metadata) {

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/metrics/BigtableTracerUnaryCallable.java

@@ -53,8 +53,8 @@ public ApiFuture futureCall(RequestT request, ApiCallContext context) {
  if (context.getTracer() instanceof BigtableTracer) {
  final GrpcResponseMetadata responseMetadata = new GrpcResponseMetadata();
  final ApiCallContext contextWithResponseMetadata = responseMetadata.addHandlers(context);
- HeaderTracerUnaryCallback callback =
- new HeaderTracerUnaryCallback((BigtableTracer) context.getTracer(), responseMetadata);
+ BigtableTracerUnaryCallback callback =
+ new BigtableTracerUnaryCallback((BigtableTracer) context.getTracer(), responseMetadata);
  ApiFuture<ResponseT> future = innerCallable.futureCall(request, contextWithResponseMetadata);
  ApiFutures.addCallback(future, callback, MoreExecutors.directExecutor());
  return future;
@@ -63,12 +63,12 @@ public ApiFuture futureCall(RequestT request, ApiCallContext context) {
  }
  }
 
- class HeaderTracerUnaryCallback<ResponseT> implements ApiFutureCallback<ResponseT> {
+ class BigtableTracerUnaryCallback<ResponseT> implements ApiFutureCallback<ResponseT> {
 
  private final BigtableTracer tracer;
  private final GrpcResponseMetadata responseMetadata;
 
- HeaderTracerUnaryCallback(BigtableTracer tracer, GrpcResponseMetadata responseMetadata) {
+ BigtableTracerUnaryCallback(BigtableTracer tracer, GrpcResponseMetadata responseMetadata) {
  this.tracer = tracer;
  this.responseMetadata = responseMetadata;
  }