Add the possibility to build with PGO when using Clang

build/config/compiler/compiler.gni

 # Copyright 2015 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/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
+import("//build/config/compiler/pgo/pgo.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")
 import("//build_overrides/build.gni")
 
 declare_args() {
   # How many symbols to include in the build. This affects the performance of
   # the build since the symbols are large and dealing with them is slow.
   #   2 means regular build with symbols.
   #   1 means minimal symbols, usually enough for backtraces only.
@@ skipping 15 matching lines @@
   # the default.  This is necessary to delay the evaluation of the default
   # value expression until after its input values such as use_gold have
   # been set, e.g. by a toolchain_args() block.
   use_debug_fission = "default"
 
   # Tell VS to create a PDB that references information in .obj files rather
   # than copying it all. This should improve linker performance. mspdbcmf.exe
   # can be used to convert a fastlink pdb to a normal one.
   is_win_fastlink = false
 
-  # Specify the current PGO phase, only used for the Windows MSVS build. Here's
-  # the different values that can be used:
-  #     0 : Means that PGO is turned off.
-  #     1 : Used during the PGI (instrumentation) phase.
-  #     2 : Used during the PGO (optimization) phase.
-  #
-  # TODO(sebmarchand): Add support for the PGU (update) phase.
-  chrome_pgo_phase = 0
-
   # Whether or not we should turn on incremental WPO. Only affects the VS
   # Windows build.
   use_incremental_wpo = false
 }
 
 declare_args() {
   # Whether or not the official builds should be built with full WPO. Enabled by
   # default for the PGO and the x64 builds.
   if (chrome_pgo_phase > 0) {
     full_wpo_on_official = true
@@ skipping 45 matching lines @@
 }
 
 # Assert that the configuration isn't going to hit https://crbug.com/648948.
 assert(ignore_elf32_limitations || !is_android ||
            (android_64bit_target_cpu && !build_apk_secondary_abi) ||
            is_component_build || symbol_level < 2 || is_clang,
        "Android 32-bit non-component, non-clang builds cannot have " +
            "symbol_level=2 due to 4GiB file size limit, see " +
            "https://crbug.com/648948. If you really want to try this out, " +
            "set ignore_elf32_limitations=true.")