Enable WPO for the x64 Official builds.

build/config/compiler/BUILD.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.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 1175 matching lines @@
   common_optimize_on_ldflags = [ "/OPT:ICF" ]  # Redundant COMDAT folding.
   if (is_official_build) {
     common_optimize_on_ldflags += [
       "/OPT:REF",  # Remove unreferenced data.
       "/LTCG",  # Link-time code generation.
 
       # Set the number of LTCG code-gen threads to eight. The default is four.
       # This gives a 5-10% link speedup.
       "/cgthreads:8",
     ]
+    if (full_wpo_on_official) {
+      arflags = [ "/LTCG" ]
+    }
   }
 } else {
   common_optimize_on_cflags = [
     # Don't emit the GCC version ident directives, they just end up in the
     # .comment section taking up binary size.
     "-fno-ident",
 
     # Put data and code in their own sections, so that unused symbols
     # can be removed at link time with --gc-sections.
     "-fdata-sections",
@@ skipping 257 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }