Add an `auto_profile_path` flag to GN to control AFDO.

build/config/BUILDCONFIG.gn

 # Copyright (c) 2013 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.
 
 # =============================================================================
 # WHAT IS THIS FILE?
 # =============================================================================
 #
 # This is the master GN build configuration. This file is loaded after the
 # build args (args.gn) for the build directory and after the toplevel ".gn"
@@ skipping 449 matching lines @@
 # =============================================================================
 #
 # Set up the default configuration for every build target of the given type.
 # The values configured here will be automatically set on the scope of the
 # corresponding target. Target definitions can add or remove to the settings
 # here as needed.
 
 # Holds all configs used for running the compiler.
 default_compiler_configs = [
   "//build/config:feature_flags",
+  "//build/config/compiler:afdo",
   "//build/config/compiler:compiler",
   "//build/config/compiler:clang_stackrealign",
   "//build/config/compiler:compiler_arm_fpu",
   "//build/config/compiler:chromium_code",
   "//build/config/compiler:default_include_dirs",
   "//build/config/compiler:default_optimization",
   "//build/config/compiler:default_stack_frames",
   "//build/config/compiler:default_symbols",
   "//build/config/compiler:no_rtti",
   "//build/config/compiler:runtime_library",
@@ skipping 160 matching lines @@
 set_defaults("component") {
   if (is_component_build) {
     configs = default_shared_library_configs
     if (is_android) {
       configs -= [ "//build/config/android:hide_native_jni_exports" ]
     }
   } else {
     configs = default_compiler_configs
   }
 }