Move sanitizer and symbol flags out of BUILDCONFIG

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 c575eb1cc1f680218a6fe220ab38ae5af4b09ec6..1aa212deab712df718a92d6bf0e00315348d2ab3 100644
--- a/build/config/sanitizers/sanitizers.gni
+++ b/build/config/sanitizers/sanitizers.gni
@@ -3,6 +3,18 @@
 # found in the LICENSE file.
 
 declare_args() {
+  # Compile for Address Sanitizer to find memory bugs.
+  is_asan = false
+
+  # Compile for Leak Sanitizer to find leaks.
+  is_lsan = false
+
+  # Compile for Memory Sanitizer to find uninitialized reads.
+  is_msan = false
+
+  # Compile for Thread Sanitizer to find threading bugs.
+  is_tsan = false
+
   # Use libc++ (buildtools/third_party/libc++ and
   # buildtools/third_party/libc++abi) instead of stdlibc++ as standard library.
   # This is intended to be used for instrumented builds.
@@ -32,6 +44,12 @@ declare_args() {
   use_cfi_diag = false
 }
 
+# TODO(GYP) bug 527515: is_ubsan, is_ubsan_vptr
+using_sanitizer = is_asan || is_lsan || is_tsan || is_msan
+
+assert(!using_sanitizer || is_clang,
+       "Sanitizers (is_*san) require setting is_clang = true in 'gn args'")
+
 # MSan only links Chrome properly in release builds (brettw -- 9/1/2015). The
 # same is possibly true for the other non-ASan sanitizers. But regardless of
 # whether it links, one would normally never run a sanitizer in debug mode.