Enable use-after-scope check in ASAN configs.

At this point, everything but Mac has been fixed. On Mac, there's an outstanding issue, which will be fixed later.

BUG=649897

Review-Url: https://codereview.chromium.org/2451973004
Cr-Original-Commit-Position: refs/heads/master@{#445114}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 866204443431a62c1b6e1404ed3c19c3f529ce45

config/sanitizers/BUILD.gn

@@ -200,6 +200,9 @@ config("default_sanitizer_ldflags") {
     ldflags = []
     if (is_asan) {
       ldflags += [ "-fsanitize=address" ]
+      if (!is_mac) {
+        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_mac) {
+      cflags += [ "-fsanitize-address-use-after-scope" ]
+    }
     if (!asan_globals) {
       cflags += [
         "-mllvm",