[Mac/GN] Implement dSYM generation and stripping.

build/config/mac/symbols.gni

+# Copyright 2016 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/chrome_build.gni")
+
+# This file declares arguments and configs that control whether dSYM debug
+# info is produced and whether build products are stripped.
+
+declare_args() {
+  # Produce dSYM files for targets that are configured to do so. By default,
+  # symbol information is retained in the object files because dsymutil is
+  # very slow. Targets interested in having a dSYM file produced can use the
+  # //build/config/mac:dsym config.
+  enable_dsyms = is_official_build
+
+  # Strip symbols from targets that are configured to do so. This should be
+  # used in conjuction with enable_dsyms to ensure that debug information
+  # remains available. The linker driver will produce any dSYMs before
+  # invoking strip. Targets that do not want to keep symbols can use the
+  # //build/config/mac:strip_all config. If targets wish to use a saves file,
+  # they should add the ldflags themselves, conditional on this argument.
+  enable_stripping = is_official_build
+}