Introduce experimental natives that are enabled by a runtime flag.

tools/gyp/v8.gyp

Index: tools/gyp/v8.gyp
diff --git a/tools/gyp/v8.gyp b/tools/gyp/v8.gyp
index 77a6194c430a2df7f66029d6b254f44db475b856..a11d19a8b5d3075589a6de04750b7e1b9f6bc4d0 100644
--- a/tools/gyp/v8.gyp
+++ b/tools/gyp/v8.gyp
@@ -230,7 +230,8 @@
             '../../src',
           ],
           'sources': [
-            '<(SHARED_INTERMEDIATE_DIR)/libraries-empty.cc',
+            '<(SHARED_INTERMEDIATE_DIR)/libraries.cc',
+            '<(SHARED_INTERMEDIATE_DIR)/experimental-libraries.cc',
             '<(INTERMEDIATE_DIR)/snapshot.cc',
           ],
           'actions': [
@@ -259,6 +260,7 @@
           ],
           'sources': [
             '<(SHARED_INTERMEDIATE_DIR)/libraries.cc',
+            '<(SHARED_INTERMEDIATE_DIR)/experimental-libraries.cc',
             '../../src/snapshot-empty.cc',
           ],
           'conditions': [
@@ -722,6 +724,10 @@
               '../../src/regexp.js',
               '../../src/macros.py',
             ],
+	    'experimental_library_files': [
+	      '../../src/proxy.js',
+              '../../src/macros.py',
+	    ],
           },
           'actions': [
             {
@@ -732,7 +738,6 @@
               ],
               'outputs': [
                 '<(SHARED_INTERMEDIATE_DIR)/libraries.cc',
-                '<(SHARED_INTERMEDIATE_DIR)/libraries-empty.cc',
               ],
               'action': [
                 'python',
@@ -742,6 +747,23 @@
                 '<@(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)'
+              ],
+            },
           ],
         },
         {