Move gtest_prod_util.h out of webrtc/test tree.

webrtc/base/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.
 
 import("//build/config/crypto.gni")
 import("//build/config/ui.gni")
@@ skipping 625 matching lines @@
       "objc/RTCLogging.h",
       "objc/RTCLogging.mm",
       "objc/RTCMacros.h",
       "objc/RTCSSLAdapter.h",
       "objc/RTCSSLAdapter.mm",
       "objc/RTCTracing.h",
       "objc/RTCTracing.mm",
     ]
   }
 }
+
+source_set("gtest_prod") {
+  sources = [
+    "gtest_prod_util.h",
+  ]
+}