Optionally export metadata with libv8 to enable debuggers to inspect V8 state.

tools/gyp/v8.gyp

Index: tools/gyp/v8.gyp
===================================================================
--- tools/gyp/v8.gyp	(revision 10572)
+++ tools/gyp/v8.gyp	(working copy)
@@ -729,6 +729,11 @@
                 'V8_SHARED',
               ],
             }],
+            ['v8_postmortem_support=="true"', {
+              'sources': [
+                '<(SHARED_INTERMEDIATE_DIR)/debug-support.cc',
+              ]
+            }],
           ],
         },
         {
@@ -805,6 +810,34 @@
           ],
         },
         {
+          'target_name': 'postmortem-metadata',
+          'type': 'none',
+          'variables': {
+            'heapobject_files': [
+                '../../src/objects.h',
+                '../../src/objects-inl.h',
+            ],
+          },
+          'actions': [
+              {
+                'action_name': 'gen-postmortem-metadata',
+                'inputs': [
+                  '../../tools/gen-postmortem-metadata.py',
+                  '<@(heapobject_files)',
+                ],
+                'outputs': [
+                  '<(SHARED_INTERMEDIATE_DIR)/debug-support.cc',
+                ],
+                'action': [
+                  'python',
+                  '../../tools/gen-postmortem-metadata.py',
+                  '<@(_outputs)',
+                  '<@(heapobject_files)'
+                ]
+              }
+           ]
+        },
+        {
           'target_name': 'mksnapshot',
           'type': 'executable',
           'dependencies': [