Enable ThinLTO cache.

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 453 matching lines @@
   # flags for specific features.
   if (!is_debug && (allow_posix_link_time_opt || is_cfi) && !is_nacl) {
     if (use_thin_lto) {
       cflags += [ "-flto=thin" ]
       ldflags += [ "-flto=thin" ]
 
       # Limit the parallelism to avoid too agressive competition between
       # linker jobs. This is still suboptimal to a potential dynamic
       # resource allocation scheme, but should be good enough.
       if (use_lld) {
-        ldflags += [ "-Wl,--thinlto-jobs=8" ]
+        ldflags += [
+          "-Wl,--thinlto-jobs=8",
+          "-Wl,--thinlto-cache-dir=" +
+              rebase_path("$root_out_dir/thinlto-cache", root_build_dir),
+        ]
       } else {
         ldflags += [ "-Wl,-plugin-opt,jobs=8" ]
       }
     } else {
       # Note: ThinLTO does not currently have this feature implemented
       # For Full LTO, it provides a measurable runtime speedup of Chrome.
       cflags += [
         "-flto",
         "-fwhole-program-vtables",
       ]
@@ skipping 1218 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
   }
 }