Introduces `ParserOptions`.

pkg/compiler/lib/src/parser/parser.dart

Index: pkg/compiler/lib/src/parser/parser.dart
diff --git a/pkg/compiler/lib/src/parser/parser.dart b/pkg/compiler/lib/src/parser/parser.dart
index 42e432becd9afb93159aeec24e8c832ec9477ad6..dc8ec5477afe7cc830af2ab709b39ce25c59304e 100644
--- a/pkg/compiler/lib/src/parser/parser.dart
+++ b/pkg/compiler/lib/src/parser/parser.dart
@@ -72,6 +72,15 @@ class FormalParameterType {
   static final NAMED = const FormalParameterType('named');
 }
 
+/// Options used for parsing.
+///
+/// Use this to conditionally support certain constructs, e.g.,
+/// experimental ones.
+class ParserOptions {
+  final bool enableConditionalDirectives;
+  const ParserOptions({this.enableConditionalDirectives: false});

[Johnni Winther, 2016/03/11 13:43:39]

Nit: Add an empty line before the constructor.

[eernst, 2016/03/21 13:03:34]

Done.

+}
+
 /**
  * An event generating parser of Dart programs. This parser expects
  * all tokens in a linked list (aka a token stream).
@@ -97,13 +106,12 @@ class FormalParameterType {
  */
 class Parser {
   final Listener listener;
+  final ParserOptions parserOptions;
   bool mayParseFunctionExpressions = true;
-  final bool enableConditionalDirectives;
   bool asyncAwaitKeywordsEnabled;
 
-  Parser(this.listener,
-      {this.enableConditionalDirectives: false,
-       this.asyncAwaitKeywordsEnabled: false});
+  Parser(this.listener, this.parserOptions,
+      {this.asyncAwaitKeywordsEnabled: false});
 
   Token parseUnit(Token token) {
     listener.beginCompilationUnit(token);
@@ -180,7 +188,7 @@ class Parser {
   Token parseConditionalUris(Token token) {
     listener.beginConditionalUris(token);
     int count = 0;
-    if (enableConditionalDirectives) {
+    if (parserOptions.enableConditionalDirectives) {
       while (optional('if', token)) {
         count++;
         token = parseConditionalUri(token);