Correct gen_date_localizations.dart supported locales computation (flutter#20920)

Author: Hans Muller

dev/tools/gen_date_localizations.dart

@@ -83,7 +83,7 @@ Future<Null> main(List<String> rawArgs) async {
 // ignore_for_file: public_member_api_docs
 '''
 );
-  buffer.writeln('const Map<String, dynamic> dateSymbols = const <String, dynamic> {');
+  buffer.writeln('const Map<String, dynamic> dateSymbols = <String, dynamic> {');
   symbolFiles.forEach((String locale, File data) {
     if (materialLocales.contains(locale))
       buffer.writeln(_jsonToMapEntry(locale, json.decode(data.readAsStringSync())));
@@ -92,11 +92,11 @@ Future<Null> main(List<String> rawArgs) async {
 
   // Code that uses datePatterns expects it to contain values of type
   // Map<String, String> not Map<String, dynamic>.
-  buffer.writeln('const Map<String, Map<String, String>> datePatterns = const <String, Map<String, String>> {');
+  buffer.writeln('const Map<String, Map<String, String>> datePatterns = <String, Map<String, String>> {');
   patternFiles.forEach((String locale, File data) {
     if (materialLocales.contains(locale)) {
       final Map<String, dynamic> patterns = json.decode(data.readAsStringSync());
-      buffer.writeln("'$locale': const <String, String>{");
+      buffer.writeln("'$locale': <String, String>{");
       patterns.forEach((String key, dynamic value) {
         assert(value is String);
         buffer.writeln(_jsonToMapEntry(key, value));
@@ -134,10 +134,10 @@ String _jsonToMap(dynamic json) {
   }
 
   if (json is Iterable)
-    return 'const <dynamic>[${json.map(_jsonToMap).join(',')}]';
+    return '<dynamic>[${json.map(_jsonToMap).join(',')}]';
 
   if (json is Map<String, dynamic>) {
-    final StringBuffer buffer = new StringBuffer('const <String, dynamic>{');
+    final StringBuffer buffer = new StringBuffer('<String, dynamic>{');
     json.forEach((String key, dynamic value) {
       buffer.writeln(_jsonToMapEntry(key, value));
     });
@@ -149,7 +149,7 @@ String _jsonToMap(dynamic json) {
 }
 
 Iterable<String> _materialLocales() sync* {
-  final RegExp filenameRE = new RegExp(r'.*_(\w+)\.arb$');
+  final RegExp filenameRE = new RegExp(r'material_(\w+)\.arb$');
   final Directory materialLocalizationsDirectory = new Directory(path.join('packages', 'flutter_localizations', 'lib', 'src', 'l10n'));
   for (FileSystemEntity entity in materialLocalizationsDirectory.listSync()) {
     final String filePath = entity.path;