[destructuring] Refactor duplicate parameter name detection.

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.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/mips.gni")
 
 # Because standalone V8 builds are not supported, assume this is part of a
 # Chromium build.
@@ skipping 764 matching lines @@
     "src/double.h",
     "src/dtoa.cc",
     "src/dtoa.h",
     "src/effects.h",
     "src/elements-kind.cc",
     "src/elements-kind.h",
     "src/elements.cc",
     "src/elements.h",
     "src/execution.cc",
     "src/execution.h",
+    "src/expression-classifier.h",
     "src/extensions/externalize-string-extension.cc",
     "src/extensions/externalize-string-extension.h",
     "src/extensions/free-buffer-extension.cc",
     "src/extensions/free-buffer-extension.h",
     "src/extensions/gc-extension.cc",
     "src/extensions/gc-extension.h",
     "src/extensions/statistics-extension.cc",
     "src/extensions/statistics-extension.h",
     "src/extensions/trigger-failure-extension.cc",
     "src/extensions/trigger-failure-extension.h",
@@ skipping 883 matching lines @@
       sources += [
         "src/d8-debug.cc",
         "$target_gen_dir/d8-js.cc",
       ]
     }
     if (v8_enable_i18n_support) {
       deps += [ "//third_party/icu" ]
     }
   }
 }