Adds ability to build for asan with gn

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
new file mode 100644
index 0000000000000000000000000000000000000000..6012b48e3a86557e728e109843fb80a3e3d0893f
--- /dev/null
+++ b/build/config/sanitizers/BUILD.gn
@@ -0,0 +1,26 @@
+# Copyright 2014 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.
+
+# Contains the dependencies needed for asan to link into executables and
+# shared_libraries. Unconditionally depend upon this target as it is empty if
+# |is_asan| is false.
+group("deps") {
+  if (is_asan) {
+    public_configs = [ ":sanitizer_options_link_helper" ]
+    deps = [ ":options_sources" ]
+  }
+}
+
+config("sanitizer_options_link_helper") {
+  ldflags = [ "-Wl,-u_sanitizer_options_link_helper", "-fsanitize=address" ]
+}
+
+source_set("options_sources") {
+  visibility = [ ":deps" ]
+  sources = [ "//build/sanitizers/sanitizer_options.cc" ]
+
+  if (is_tsan) {
+    sources += [ "//build/sanitizers/tsan_suppressions.cc" ]
+  }
+}