Add a new gyp flag: fieldtrial_testing_like_official_build

build/config/BUILD.gn

 # Copyright (c) 2013 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/allocator.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
@@ skipping 266 matching lines @@
   if (enable_webvr) {
     defines += [ "ENABLE_WEBVR" ]
   }
   if (is_syzyasan) {
     defines += [
       "SYZYASAN",
       "MEMORY_TOOL_REPLACES_ALLOCATOR",
       "MEMORY_SANITIZER_INITIAL_SIZE",
     ]
   }
+  if (!fieldtrial_testing_like_official_build && !is_chrome_branded) {
+    defines += [ "FIELDTRIAL_TESTING_ENABLED" ]
+  }
 }
 
 # Debug/release ----------------------------------------------------------------
 
 config("debug") {
   defines = [
     "_DEBUG",
     "DYNAMIC_ANNOTATIONS_ENABLED=1",
     "WTF_USE_DYNAMIC_ANNOTATIONS=1",
   ]
@@ skipping 141 matching lines @@
     # with precompiled headers since the source file that's "compiled" for
     # making the precompiled header is empty.
     #
     # This error doesn't happen every time. In VS2013, it seems if the .pch
     # file doesn't exist, no error will be generated (probably MS tested this
     # case but forgot the other one?). To reproduce this error, do a build,
     # then delete the precompile.c.obj file, then build again.
     cflags_c = [ "/wd4206" ]
   }
 }