Enable ES6 Map and Set by default

BUILD.gn

 # Copyright 2014 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.
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
 v8_compress_startup_data = "off"
 v8_deprecation_warnings = false
 v8_enable_disassembler = false
 v8_enable_gdbjit = false
@@ skipping 174 matching lines @@
 
   # The script depends on this other script, this rule causes a rebuild if it
   # changes.
   source_prereqs = [ "tools/jsmin.py" ]
 
   sources = [
     "src/runtime.js",
     "src/v8natives.js",
     "src/array.js",
     "src/string.js",
+    "src/symbol.js",
     "src/uri.js",
     "src/math.js",
     "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/arraybuffer.js",
     "src/typedarray.js",
+    "src/collection.js",
+    "src/collection-iterator.js",
     "src/weak_collection.js",
     "src/promise.js",
     "src/object-observe.js",
     "src/macros.py",
   ]
 
   outputs = [
     "$target_gen_dir/libraries.cc"
   ]
 
@@ skipping 20 matching lines @@
   visibility = ":*"  # Only targets in this file can depend on this.
 
   script = "tools/js2c.py"
 
   # The script depends on this other script, this rule causes a rebuild if it
   # changes.
   source_prereqs = [ "tools/jsmin.py" ]
 
   sources = [
     "src/macros.py",
-    "src/symbol.js",
     "src/proxy.js",
-    "src/collection.js",
-    "src/collection-iterator.js",
     "src/generator.js",
     "src/array-iterator.js",
     "src/harmony-string.js",
     "src/harmony-array.js",
   ]
 
   outputs = [
     "$target_gen_dir/experimental-libraries.cc"
   ]
 
@@ skipping 1024 matching lines @@
     deps = [
       ":v8_base",
       ":v8_nosnapshot",
     ]
   }
 
   direct_dependent_configs = [ ":external_config" ]
 }
 
 }