Enable use-after-scope check in ASAN configs.

build/config/sanitizers/BUILD.gn

Index: build/config/sanitizers/BUILD.gn
diff --git a/build/config/sanitizers/BUILD.gn b/build/config/sanitizers/BUILD.gn
index e7425461d40b6cdf5aab428f0adf66ba934dde13..e314aa8e422b1fe302a0130c6be27eab8e7ffcdf 100644
--- a/build/config/sanitizers/BUILD.gn
+++ b/build/config/sanitizers/BUILD.gn
@@ -200,6 +200,9 @@ config("default_sanitizer_ldflags") {
     ldflags = []
     if (is_asan) {
       ldflags += [ "-fsanitize=address" ]
+      if (is_clang && !is_mac && !is_chromeos && !is_win) {

[Nico, 2017/01/23 22:25:20]

this is in is_posix, you don't need !is_win here.

also, doesn't is_asan imply is_clang?

[krasin1, 2017/01/23 22:31:51]

well, apparently, clang-cl is considered to be posix. See
https://crbug.com/683966
Well, I also thought that is_asan implies the single Clang version, which proved
to be not the case for Chrome OS, see https://crbug.com/683445. Now, I don't
want to make strong assumptions. I need clang, I have put is_clang.

[Nico, 2017/01/23 22:35:02]

That's from asan_flags below, not from default_sanitizer_ld_flags, right?
Hm, I'd prefer if we pretend that we know what's going on even if it means
another round of reverts. That seems better than adding lots of just-in-case
code all over the place.

[krasin1, 2017/01/23 22:49:54]

ah, right.
that's a valid point. I have removed is_clang.

+        ldflags += [ "-fsanitize-address-use-after-scope" ]
+      }
     }
     if (is_lsan) {
       ldflags += [ "-fsanitize=leak" ]
@@ -309,6 +312,9 @@ config("asan_flags") {
   cflags = []
   if (is_asan) {
     cflags += [ "-fsanitize=address" ]
+    if (is_clang && !is_mac && !is_chromeos && !is_win) {
+      cflags += [ "-fsanitize-address-use-after-scope" ]
+    }
     if (!asan_globals) {
       cflags += [
         "-mllvm",