Replace uses of JSON constant in intl and intl_translation

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=192172678
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5ad2863..82ec07e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
  * Add type parameters on numberFormatSymbols for Dart 2 compatibility. Note
    that it only adds them on the right-hand side because adding them to the
    static type can cause unnecessary cast warnings.
+ * Replace uses of JSON constant for Dart 2 compatibility.
 
 ## 0.15.4
  * A couple of minor Dart 2 fixes.
diff --git a/lib/src/lazy_locale_data.dart b/lib/src/lazy_locale_data.dart
index 07d46f7..b975a4e 100644
--- a/lib/src/lazy_locale_data.dart
+++ b/lib/src/lazy_locale_data.dart
@@ -35,6 +35,8 @@
   /// The set of available locales.
   Set availableLocaleSet;
 
+  static const jsonDecoder = const JsonCodec();
+
   /// The constructor. The [_reader] specifies where the data comes
   /// from. The [_creationFunction] creates the appropriate data type
   /// from the remote data (which typically comes in as a Map). The
@@ -90,6 +92,6 @@
   /// Given a Future [input] whose value is expected to be a string in JSON
   /// form, return another future that parses the JSON into a usable format.
   Future jsonData(Future input) {
-    return input.then((response) => JSON.decode(response));
+    return input.then((response) => jsonDecoder.decode(response));
   }
 }
diff --git a/tool/generate_locale_data_files.dart b/tool/generate_locale_data_files.dart
index 2fde04b..498d405 100644
--- a/tool/generate_locale_data_files.dart
+++ b/tool/generate_locale_data_files.dart
@@ -67,10 +67,10 @@
 void writePatterns(locale, patterns) {
   var file = new File(path.join(dataDirectory, 'patterns', '${locale}.json'));
   file.openWrite()
-    ..write(JSON.encode(patterns))
+    ..write(new JsonCodec().encode(patterns))
     ..close();
 }
 
 void writeToJSON(dynamic data, IOSink out) {
-  out.write(JSON.encode(data.serializeToMap()));
+  out.write(new JsonCodec().encode(data.serializeToMap()));
 }