Revert "Add optional message to assert in Dart2js - continued"

pkg/compiler/lib/src/inferrer/inferrer_visitor.dart

Index: pkg/compiler/lib/src/inferrer/inferrer_visitor.dart
diff --git a/pkg/compiler/lib/src/inferrer/inferrer_visitor.dart b/pkg/compiler/lib/src/inferrer/inferrer_visitor.dart
index 08fa94517b41c3e90569a3ab0e8f72093c5fb3e4..482eb115544bffe517a66fa2329e014287e7354f 100644
--- a/pkg/compiler/lib/src/inferrer/inferrer_visitor.dart
+++ b/pkg/compiler/lib/src/inferrer/inferrer_visitor.dart
@@ -758,14 +758,6 @@ abstract class InferrerVisitor<T, E extends MinimalInferrerEngine<T>>
 
   T handleDynamicInvoke(Send node);
 
-  T visitAssert(Assert node) {
-    // Avoid pollution from assert statement unless enabled.
-    if (compiler.enableUserAssertions) {
-      super.visitAssert(node);
-    }
-    return null;
-  }
-
   T visitAsyncForIn(AsyncForIn node);
 
   T visitSyncForIn(SyncForIn node);
@@ -804,6 +796,17 @@ abstract class InferrerVisitor<T, E extends MinimalInferrerEngine<T>>
     return types.dynamicType;
   }
 
+  @override
+  T visitAssert(Send node, Node expression, _) {
+    if (!compiler.enableUserAssertions) {
+      return types.nullType;
+    }
+    return handleAssert(node, expression);
+  }
+
+  /// Handle an enabled assertion of [expression].
+  T handleAssert(Send node, Node expression);
+
   T visitNode(Node node) {
     return node.visitChildren(this);
   }