Expose counters in javascript.

src/SConscript

 # Copyright 2012 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 54 matching lines @@
     debug.cc
     deoptimizer.cc
     disassembler.cc
     diy-fp.cc
     dtoa.cc
     elements-kind.cc
     elements.cc
     execution.cc
     extensions/externalize-string-extension.cc
     extensions/gc-extension.cc
+    extensions/counters-extension.cc
     factory.cc
     fast-dtoa.cc
     fixed-dtoa.cc
     flags.cc
     frames.cc
     full-codegen.cc
     func-name-inferrer.cc
     gdb-jit.cc
     global-handles.cc
     handles.cc
@@ skipping 317 matching lines @@
       snapshot_cc = 'snapshot.cc'
     snapshot_obj = context.ConfigureObject(env, snapshot_cc, CPPPATH=['.'])
   else:
     snapshot_obj = empty_snapshot_obj
   library_objs = [non_snapshot_files, libraries_obj, experimental_libraries_obj, snapshot_obj]
   return (library_objs, d8_objs, [mksnapshot], preparser_objs)
 
 
 (library_objs, d8_objs, mksnapshot, preparser_objs) = ConfigureObjectFiles()
 Return('library_objs d8_objs mksnapshot preparser_objs')