GN: Don't build tests by default.

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("webrtc/build/webrtc.gni")
+
 group("default") {
   testonly = true
   deps = [
     "//webrtc",
-    "//webrtc:webrtc_tests",
-    "//webrtc/examples",
-    "//webrtc/tools",
   ]
+  if (rtc_include_tests) {
+    deps += [
+      "//webrtc:webrtc_tests",
+      "//webrtc/examples",
+      "//webrtc/tools",
+    ]
+  }
 }