Fix recursion bug in blocking a fetch and add a test

headless/public/util/testing/generic_url_request_mocks.cc

 // 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.
 
 #include "headless/public/util/testing/generic_url_request_mocks.h"
 
 #include "base/logging.h"
 
 namespace net {
 class URLRequestJob;
 }  // namespace net
 
 namespace headless {
 
 // MockGenericURLRequestJobDelegate
-MockGenericURLRequestJobDelegate::MockGenericURLRequestJobDelegate() {}
+MockGenericURLRequestJobDelegate::MockGenericURLRequestJobDelegate()
+    : should_block_(false) {}
 MockGenericURLRequestJobDelegate::~MockGenericURLRequestJobDelegate() {}
 
 bool MockGenericURLRequestJobDelegate::BlockOrRewriteRequest(
     const GURL& url,
     const std::string& referrer,
     GenericURLRequestJob::RewriteCallback callback) {
-  return false;
+  if (should_block_)
+    callback(GenericURLRequestJob::RewriteResult::kDeny, GURL());
+  return should_block_;
 }
 
 const GenericURLRequestJob::HttpResponse*
 MockGenericURLRequestJobDelegate::MaybeMatchResource(
     const GURL& url,
     const net::HttpRequestHeaders& request_headers) {
   return nullptr;
 }
 
 void MockGenericURLRequestJobDelegate::OnResourceLoadComplete(
@@ skipping 124 matching lines @@
                                              int bytes_read) {}
 const std::string& MockURLRequestDelegate::response_data() const {
   return response_data_;
 }
 
 const net::IOBufferWithSize* MockURLRequestDelegate::metadata() const {
   return nullptr;
 }
 
 }  // namespace headless