Add support for link repros and use it on net_perftests.

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")
@@ skipping 26 matching lines @@
   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
 
   # Whether or not we should turn on incremental WPO. Only affects the VS
   # Windows build.
   use_incremental_wpo = false
+
+  # Root directory the will store the MSVC link repro. This should only be used

[scottmg, 2016/12/13 00:03:23]

"the will store" -> "that will store" (?)

[Sébastien Marchand, 2016/12/13 00:14:26]

Done.

+  # for debugging purposes on the builders where a MSVC linker flakyness has
+  # been observed. The targets for which a link repro should be generated
+  # should add somethink like this to their configuration:

[scottmg, 2016/12/13 00:03:23]

somethink -> something

[Sébastien Marchand, 2016/12/13 00:14:26]

Ark, 2 typos in 5 lines, sorry for that.

+  #   if (linkrepro_root_dir != "") {
+  #     ldflags = ["/LINKREPRO:" + linkrepro_root_dir + "/" + target_name]
+  #   }
+  #
+  # Note that doing a link repro uses a lot of disk space and slow down the

[scottmg, 2016/12/13 00:03:23]

slow -> slows

[Sébastien Marchand, 2016/12/13 00:14:26]

Done.

+  # build, so this shouldn't be enabled on too many targets.

[scottmg, 2016/12/13 00:03:23]

Add a crbug link here.

[Sébastien Marchand, 2016/12/13 00:14:26]

Done.

+  linkrepro_root_dir = ""
 }
 
 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
   } else {
     full_wpo_on_official = false
   }
@@ skipping 42 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.")