Reland of "Decoupling rtc_base from Obj-C code"

webrtc/rtc_base/noop.mm

Index: webrtc/rtc_base/noop.mm
diff --git a/webrtc/rtc_base/noop.mm b/webrtc/rtc_base/noop.mm
new file mode 100644
index 0000000000000000000000000000000000000000..16a8e6d5c10b97134e68b08e2c65ef2fff16bd52
--- /dev/null
+++ b/webrtc/rtc_base/noop.mm
@@ -0,0 +1,13 @@
+/*
+ *  Copyright 2015 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.
+ */
+
+// This file is only needed to make ninja happy on some platforms.
+// On some platforms it is not possible to link an rtc_static_library
+// without any source file listed in the GN target.