Introduce experimental natives that are enabled by a runtime flag.

tools/gyp/v8.gyp

 # Copyright 2011 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 212 matching lines @@
           ],
           'dependencies': [
             'mksnapshot#host',
             'js2c#host',
             'v8_base',
           ],
           'include_dirs+': [
             '../../src',
           ],
           'sources': [
-            '<(SHARED_INTERMEDIATE_DIR)/libraries-empty.cc',
+            '<(SHARED_INTERMEDIATE_DIR)/libraries.cc',
+            '<(SHARED_INTERMEDIATE_DIR)/experimental-libraries.cc',
             '<(INTERMEDIATE_DIR)/snapshot.cc',
           ],
           'actions': [
             {
               'action_name': 'run_mksnapshot',
               'inputs': [
                 '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)mksnapshot<(EXECUTABLE_SUFFIX)',
               ],
               'outputs': [
                 '<(INTERMEDIATE_DIR)/snapshot.cc',
               ],
               'action': ['<@(_inputs)', '<@(_outputs)'],
             },
           ],
         },
         {
           'target_name': 'v8_nosnapshot',
           'type': '<(library)',
           'toolsets': ['host', 'target'],
           'dependencies': [
             'js2c#host',
             'v8_base',
           ],
           'include_dirs+': [
             '../../src',
           ],
           'sources': [
             '<(SHARED_INTERMEDIATE_DIR)/libraries.cc',
+            '<(SHARED_INTERMEDIATE_DIR)/experimental-libraries.cc',
             '../../src/snapshot-empty.cc',
           ],
           'conditions': [
             # The ARM assembler assumes the host is 32 bits, so force building
             # 32-bit host tools.
             ['v8_target_arch=="arm" and host_arch=="x64" and _toolset=="host"', {
               'cflags': ['-m32'],
               'ldflags': ['-m32'],
             }],
             ['OS=="win" and component=="shared_library"', {
@@ skipping 443 matching lines @@
               '../../src/messages.js',
               '../../src/apinatives.js',
               '../../src/debug-debugger.js',
               '../../src/mirror-debugger.js',
               '../../src/liveedit-debugger.js',
               '../../src/date.js',
               '../../src/json.js',
               '../../src/regexp.js',
               '../../src/macros.py',
             ],
+            'experimental_library_files': [
+              '../../src/proxy.js',
+              '../../src/macros.py',
+            ],
           },
           'actions': [
             {
               'action_name': 'js2c',
               'inputs': [
                 '../../tools/js2c.py',
                 '<@(library_files)',
               ],
               'outputs': [
                 '<(SHARED_INTERMEDIATE_DIR)/libraries.cc',
-                '<(SHARED_INTERMEDIATE_DIR)/libraries-empty.cc',
               ],
               'action': [
                 'python',
                 '../../tools/js2c.py',
                 '<@(_outputs)',
                 'CORE',
                 '<@(library_files)'
               ],
             },
+            {
+              'action_name': 'js2c_experimental',
+              'inputs': [
+                '../../tools/js2c.py',
+                '<@(experimental_library_files)',
+              ],
+              'outputs': [
+                '<(SHARED_INTERMEDIATE_DIR)/experimental-libraries.cc',
+              ],
+              'action': [
+                'python',
+                '../../tools/js2c.py',
+                '<@(_outputs)',
+                'EXPERIMENTAL',
+                '<@(experimental_library_files)'
+              ],
+            },
           ],
         },
         {
           'target_name': 'mksnapshot',
           'type': 'executable',
           'toolsets': ['host'],
           'dependencies': [
             'v8_nosnapshot',
           ],
           'include_dirs+': [
@@ skipping 43 matching lines @@
           'target_name': 'v8_shell',
           'type': 'none',
           'dependencies': [
             'v8'
           ],
         },
       ],
     }],
   ],
 }