Add mac_write_linker_maps gyp define.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 1074 matching lines @@
 
     # These two variables can be set in GYP_DEFINES while running
     # |gclient runhooks| to let clang run a plugin in every compilation.
     # Only has an effect if 'clang=1' is in GYP_DEFINES as well.
     # Example:
     #     GYP_DEFINES='clang=1 clang_load=/abs/path/to/libPrintFunctionNames.dylib clang_add_plugin=print-fns' gclient runhooks
 
     'clang_load%': '',
     'clang_add_plugin%': '',
 
+    # Tell ld64 to write map files describing binary layout. Useful
+    # for looking at what contributes to binary size, e.g. with
+    # https://github.com/nico/bloat
+    'mac_write_linker_maps%': 0,
+
     # The default type of gtest.
     'gtest_target_type%': 'executable',
 
     # Enable sampling based profiler.
     # See http://google-perftools.googlecode.com/svn/trunk/doc/cpuprofile.html
     'profiling%': '0',
     # Profile without optimizing out stack frames when profiling==1.
     'profiling_full_stack_frames%': '0',
 
     # And if we want to dump symbols for Breakpad-enabled builds.
@@ skipping 2980 matching lines @@
           ['_type!="static_library"', {
             'xcode_settings': {'OTHER_LDFLAGS': ['-Wl,-search_paths_first']},
             'conditions': [
               ['asan==1', {
                 'xcode_settings': {
                   'OTHER_LDFLAGS': [
                     '-fsanitize=address',
                   ],
                 },
               }],
+              ['mac_write_linker_maps==1', {
+                'xcode_settings': {
+                  'OTHER_LDFLAGS': [
+                    '-Wl,-map,>(_target_name).map',
+                  ],
+                },
+              }],
             ],
           }],
           ['_mac_bundle', {
             'xcode_settings': {'OTHER_LDFLAGS': ['-Wl,-ObjC']},
             'target_conditions': [
               ['_type=="executable"', {
                 'conditions': [
                   ['asan==1', {
                     'postbuilds': [
                       {
@@ skipping 676 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }