GN: Build with a custom libc++ when using ASAN, TSAN or MSAN.

build/config/sanitizers/sanitizers.gni

Index: build/config/sanitizers/sanitizers.gni
diff --git a/build/config/sanitizers/sanitizers.gni b/build/config/sanitizers/sanitizers.gni
index 96e23facf844d224e039816e3e524d8cb27c6fc3..1ee5a33c950452c28df6906b804d71a53f2ec840 100644
--- a/build/config/sanitizers/sanitizers.gni
+++ b/build/config/sanitizers/sanitizers.gni
@@ -12,4 +12,9 @@ declare_args() {
   # standard system libraries. Set this flag to download prebuilt binaries from
   # GCS.
   use_prebuilt_instrumented_libraries = false
+
+  # Use libc++ (buildtools/third_party/libc++ and
+  # buildtools/third_party/libc++abi) instead of stdlibc++ as standard library.
+  # This is intended to use for instrumented builds.

[earthdok, 2015/05/25 15:28:00]

Please fix the wording here ("intended to be used").

[Sam McNally, 2015/05/26 01:15:00]

Done.

+  use_custom_libcxx = (is_asan && is_desktop_linux) || is_tsan || is_msan

[Alexander Potapenko, 2015/05/25 08:27:18]

Is 'is_desktop_linux' in GN the same as 'OS=="linux" and chromeos==0' in GYP?

[Sam McNally, 2015/05/25 08:31:22]

Yes. It's defined in
https://code.google.com/p/chromium/codesearch/#chromium/src/build/config/BUIL....

[earthdok, 2015/05/25 15:28:00]

This is disabled on CrOS because of GYP-related issues:
http://crbug.com/396979

You should be able to enable it in GN.

If you'd rather have GN mirror the GYP configuration exactly, then please put a
TODO here. Once GYP is gone (or the issue is fixed), we can replace
is_desktop_linux with is_linux.

[Sam McNally, 2015/05/26 01:15:00]

Done.

 }