[json parser] add position to error message.

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")
 import("//build/config/sanitizers/sanitizers.gni")
 
 if (is_android) {
@@ skipping 1112 matching lines @@
     "src/interpreter/handler-table-builder.h",
     "src/interpreter/interpreter.cc",
     "src/interpreter/interpreter.h",
     "src/interpreter/register-translator.cc",
     "src/interpreter/register-translator.h",
     "src/interpreter/source-position-table.cc",
     "src/interpreter/source-position-table.h",
     "src/isolate-inl.h",
     "src/isolate.cc",
     "src/isolate.h",
+    "src/json-parser.h",
     "src/json-stringifier.h",
     "src/key-accumulator.h",
     "src/key-accumulator.cc",
     "src/layout-descriptor-inl.h",
     "src/layout-descriptor.cc",
     "src/layout-descriptor.h",
     "src/list-inl.h",
     "src/list.h",
     "src/log-inl.h",
     "src/log-utils.cc",
@@ skipping 15 matching lines @@
     "src/objects-printer.cc",
     "src/objects.cc",
     "src/objects.h",
     "src/optimizing-compile-dispatcher.cc",
     "src/optimizing-compile-dispatcher.h",
     "src/ostreams.cc",
     "src/ostreams.h",
     "src/parsing/expression-classifier.h",
     "src/parsing/func-name-inferrer.cc",
     "src/parsing/func-name-inferrer.h",
-    "src/parsing/json-parser.h",
     "src/parsing/parameter-initializer-rewriter.cc",
     "src/parsing/parameter-initializer-rewriter.h",
     "src/parsing/parser-base.h",
     "src/parsing/parser.cc",
     "src/parsing/parser.h",
     "src/parsing/pattern-rewriter.cc",
     "src/parsing/preparse-data-format.h",
     "src/parsing/preparse-data.cc",
     "src/parsing/preparse-data.h",
     "src/parsing/preparser.cc",
@@ skipping 809 matching lines @@
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
   configs += [
     ":internal_config",
     ":features",
     ":toolchain",
   ]
 }