[Tracing] Make TracingCategoryObserver v8 internal.

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/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
@@ skipping 834 matching lines @@
 
   sources = [
     "//base/trace_event/common/trace_event_common.h",
 
     ### gcmole(all) ###
     "include/v8-debug.h",
     "include/v8-experimental.h",
     "include/v8-platform.h",
     "include/v8-profiler.h",
     "include/v8-testing.h",
-    "include/v8-tracing.h",
     "include/v8-util.h",
     "include/v8-version.h",
     "include/v8.h",
     "include/v8config.h",
     "src/accessors.cc",
     "src/accessors.h",
     "src/address-map.cc",
     "src/address-map.h",
     "src/allocation-site-scopes.cc",
     "src/allocation-site-scopes.h",
@@ skipping 2114 matching lines @@
   ]
 
   configs = [
     ":external_config",
     ":internal_config_base",
   ]
 }
 
 v8_fuzzer("wasm_data_section_fuzzer") {
 }