Reland of Moving webrtc.gni up one level from build/

webrtc/system_wrappers/BUILD.gn

 # Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
 }
-import("../build/webrtc.gni")
+import("../webrtc.gni")
 
 rtc_static_library("system_wrappers") {
   sources = [
     "include/aligned_array.h",
     "include/aligned_malloc.h",
     "include/atomic32.h",
     "include/clock.h",
     "include/cpu_features_wrapper.h",
     "include/cpu_info.h",
     "include/critical_section_wrapper.h",
@@ skipping 172 matching lines @@
       "//testing/gtest",
     ]
 
     if (is_android) {
       deps += [ "//testing/android/native_test:native_test_support" ]
 
       shard_timeout = 900
     }
   }
 }