Land Alexander's change that turns assert into a keyword.

lib/compiler/implementation/scanner/listener.dart

Index: lib/compiler/implementation/scanner/listener.dart
diff --git a/lib/compiler/implementation/scanner/listener.dart b/lib/compiler/implementation/scanner/listener.dart
index 86d088ccf046b8528bc26ee08fb12eecf63370b6..424d17f85b17f9c4ae2cb5fa442f061d4c526f74 100644
--- a/lib/compiler/implementation/scanner/listener.dart
+++ b/lib/compiler/implementation/scanner/listener.dart
@@ -436,6 +436,9 @@ class Listener {
   void handleEmptyStatement(Token token) {
   }
 
+  void handleAssertStatement(Token assertKeyword, Token semicolonToken) {
+  }
+
   /** Called with either the token containing a double literal, or
     * an immediately preceding "unary plus" token.
     */
@@ -1697,6 +1700,13 @@ class NodeListener extends ElementListener {
                                 beginToken, inKeyword));
   }
 
+  void handleAssertStatement(Token assertKeyword, Token semicolonToken) {
+    NodeList arguments = popNode();
+    Node selector = new Identifier(assertKeyword);
+    Node send = new Send(null, selector, arguments);
+    pushNode(new ExpressionStatement(send, semicolonToken));
+  }
+
   void endUnamedFunction(Token token) {
     Statement body = popNode();
     NodeList formals = popNode();