Implement initializer asserts.

pkg/front_end/lib/src/fasta/parser/listener.dart

Index: pkg/front_end/lib/src/fasta/parser/listener.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/listener.dart b/pkg/front_end/lib/src/fasta/parser/listener.dart
index 1ac2b7f3dc52e791634f59ab7670d7c8fcf7a2e4..fb84787c65466e0b63a34cbc9d7e3446845da7bf 100644
--- a/pkg/front_end/lib/src/fasta/parser/listener.dart
+++ b/pkg/front_end/lib/src/fasta/parser/listener.dart
@@ -10,7 +10,7 @@ import '../../scanner/token.dart' show BeginToken, Token, TokenType;
 
 import '../util/link.dart' show Link;
 
-import 'parser.dart' show FormalParameterType, MemberKind;
+import 'parser.dart' show Assert, FormalParameterType, MemberKind;
 
 import 'identifier_context.dart' show IdentifierContext;
 
@@ -168,11 +168,19 @@ class Listener {
   void beginExpressionStatement(Token token) {}
 
   /// Called by [ClassMemberParser] after skipping an expression as error
-  /// recovery.
-  void handleRecoverExpression(Token token) {
+  /// recovery. For a stack-based listener, the suggested action is to push
+  /// `null` or a synthetic erroneous expression.
+  void handleRecoverExpression(Token token, FastaMessage message) {
     logEvent("RecoverExpression");
   }
 
+  /// Called by [Parser] after parsing an extraneous expression as error
+  /// recovery. For a stack-based listener, the suggested action is to discard
+  /// an expression from the stack.
+  void handleExtraneousExpression(Token token, FastaMessage message) {
+    logEvent("ExtraneousExpression");
+  }
+
   void endExpressionStatement(Token token) {
     logEvent("ExpressionStatement");
   }
@@ -857,9 +865,11 @@ class Listener {
     logEvent("EmptyStatement");
   }
 
-  void handleAssertStatement(Token assertKeyword, Token leftParenthesis,
+  void beginAssert(Token assertKeyword, Assert kind) {}
+
+  void endAssert(Token assertKeyword, Assert kind, Token leftParenthesis,
       Token commaToken, Token rightParenthesis, Token semicolonToken) {
-    logEvent("AssertStatement");
+    logEvent("Assert");
   }
 
   /** Called with either the token containing a double literal, or