Update vendored dependencies

This includes github.com/kurin/blazer 0.2.0, which resolves #1291

vendor/cloud.google.com/go/trace/grpc.go

@@ -29,10 +29,16 @@ const grpcMetadataKey = "grpc-trace-bin"
 // GRPCClientInterceptor returns a grpc.UnaryClientInterceptor that traces all outgoing requests from a gRPC client.
 // The calling context should already have a *trace.Span; a child span will be
 // created for the outgoing gRPC call. If the calling context doesn't have a span,
-// the call will not be traced.
+// the call will not be traced. If the client is nil, then the interceptor just
+// passes through the request.
 //
 // The functionality in gRPC that this feature relies on is currently experimental.
 func (c *Client) GRPCClientInterceptor() grpc.UnaryClientInterceptor {
+	if c == nil {
+		return func(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
+			return invoker(ctx, method, req, reply, cc, opts...)
+		}
+	}
 	return grpc.UnaryClientInterceptor(c.grpcUnaryInterceptor)
 }
 
@@ -75,8 +81,15 @@ func (c *Client) grpcUnaryInterceptor(ctx context.Context, method string, req, r
 //
 //	span := trace.FromContext(ctx)
 //
+// If the client is nil, then the interceptor just invokes the handler.
+//
 // The functionality in gRPC that this feature relies on is currently experimental.
 func (c *Client) GRPCServerInterceptor() grpc.UnaryServerInterceptor {
+	if c == nil {
+		return func(ctx context.Context, req interface{}, _ *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
+			return handler(ctx, req)
+		}
+	}
 	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp interface{}, err error) {
 		md, _ := metadata.FromIncomingContext(ctx)
 		var traceHeader string

vendor/cloud.google.com/go/trace/http.go

@@ -69,6 +69,9 @@ func (t Transport) base() http.RoundTripper {
 //
 // The span will be auto finished by the handler.
 func (c *Client) HTTPHandler(h http.Handler) http.Handler {
+	if c == nil {
+		return h
+	}
 	return &handler{traceClient: c, handler: h}
 }
 
@@ -101,5 +104,4 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set(httpHeader, spanHeader(traceID, parentSpanID, span.trace.localOptions))
 	}
 	h.handler.ServeHTTP(w, r)
-
 }

vendor/cloud.google.com/go/trace/trace.go

@@ -254,7 +254,8 @@ func nextTraceID() string {
 	return fmt.Sprintf("%016x%016x", id1, id2)
 }
 
-// Client is a client for uploading traces to the Google Stackdriver Trace server.
+// Client is a client for uploading traces to the Google Stackdriver Trace service.
+// A nil Client will no-op for all of its methods.
 type Client struct {
 	service   *api.Service
 	projectID string
@@ -310,13 +311,13 @@ func (c *Client) SetSamplingPolicy(p SamplingPolicy) {
 	}
 }
 
-// SpanFromHeader returns a new trace span, based on a provided request header
-// value. See https://cloud.google.com/trace/docs/faq.
-//
-// It returns nil iff the client is nil.
+// SpanFromHeader returns a new trace span based on a provided request header
+// value or nil iff the client is nil.
 //
 // The trace information and identifiers will be read from the header value.
 // Otherwise, a new trace ID is made and the parent span ID is zero.
+// For the exact format of the header value, see
+// https://cloud.google.com/trace/docs/support#how_do_i_force_a_request_to_be_traced
 //
 // The name of the new span is provided as an argument.
 //
@@ -352,9 +353,8 @@ func (c *Client) SpanFromHeader(name string, header string) *Span {
 	return span
 }
 
-// SpanFromRequest returns a new trace span for an HTTP request.
-//
-// It returns nil iff the client is nil.
+// SpanFromRequest returns a new trace span for an HTTP request or nil
+// iff the client is nil.
 //
 // If the incoming HTTP request contains a trace context header, the trace ID,
 // parent span ID, and tracing options will be read from that header.
@@ -390,7 +390,8 @@ func (c *Client) SpanFromRequest(r *http.Request) *Span {
 	return span
 }
 
-// NewSpan returns a new trace span with the given name.
+// NewSpan returns a new trace span with the given name or nil iff the
+// client is nil.
 //
 // A new trace and span ID is generated to trace the span.
 // Returned span need to be finished by calling Finish or FinishWait.