Add a second format to the tracing json/begin_recording endpoint.

content/test/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
@@ skipping 1316 matching lines @@
     "../browser/shared_worker/shared_worker_instance_unittest.cc",
     "../browser/shared_worker/shared_worker_service_impl_unittest.cc",
     "../browser/site_instance_impl_unittest.cc",
     "../browser/ssl/ssl_manager_unittest.cc",
     "../browser/startup_task_runner_unittest.cc",
     "../browser/storage_partition_impl_map_unittest.cc",
     "../browser/storage_partition_impl_unittest.cc",
     "../browser/streams/stream_unittest.cc",
     "../browser/streams/stream_url_request_job_unittest.cc",
     "../browser/tracing/background_tracing_config_unittest.cc",
+    "../browser/tracing/tracing_ui_unittest.cc",
     "../browser/web_contents/aura/overscroll_navigation_overlay_unittest.cc",
     "../browser/web_contents/aura/overscroll_window_animation_unittest.cc",
     "../browser/web_contents/aura/overscroll_window_delegate_unittest.cc",
     "../browser/web_contents/web_contents_delegate_unittest.cc",
     "../browser/web_contents/web_contents_impl_unittest.cc",
     "../browser/web_contents/web_contents_user_data_unittest.cc",
     "../browser/web_contents/web_contents_view_aura_unittest.cc",
     "../browser/web_contents/web_contents_view_mac_unittest.mm",
     "../browser/web_contents/web_drag_dest_mac_unittest.mm",
     "../browser/web_contents/web_drag_source_mac_unittest.mm",
@@ skipping 552 matching lines @@
   if (is_android) {
     deps += [ "//testing/android/native_test:native_test_native_code" ]
   }
 }
 
 group("fuzzers") {
   deps = [
     "//content/test/fuzzer",
   ]
 }