Add a sanitizer.gni import to the GN build.

BUILD.gn

 # 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.
 
 import("//build/config/arm.gni")
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
+import("//build/config/sanitizers/sanitizers.gni")
 import("//third_party/libvpx/libvpx_srcs.gni")
 import("//third_party/yasm/yasm_assemble.gni")
 
 # Sets the architecture name for building libvpx.
 if (current_cpu == "x86") {
   cpu_arch_full = "ia32"
 } else if (current_cpu == "x64") {
   if (is_msan) {
     cpu_arch_full = "generic"
   } else {
@@ skipping 248 matching lines @@
   }
   if (is_android) {
     deps += [ "//third_party/android_tools:cpu_features" ]
   }
   if (current_cpu == "arm") {
     deps += [ ":libvpx_assembly_arm" ]
   }
 
   public_configs = [ ":libvpx_external_config" ]
 }