Add optional message to assert in Dart2js.

pkg/compiler/lib/src/typechecker.dart

Index: pkg/compiler/lib/src/typechecker.dart
diff --git a/pkg/compiler/lib/src/typechecker.dart b/pkg/compiler/lib/src/typechecker.dart
index 74b9659d39e1bf3c60dc4a426305e3ca51a394d2..3b075b0d0692b6b621f8584f77e0d489673cb870 100644
--- a/pkg/compiler/lib/src/typechecker.dart
+++ b/pkg/compiler/lib/src/typechecker.dart
@@ -602,6 +602,12 @@ class TypeCheckerVisitor extends Visitor<DartType> {
     return type;
   }
 
+  DartType visitAssert(Assert node) {
+    analyze(node.condition);
+    if (node.hasMessage) analyze(node.message);
+    return const StatementType();
+  }
+
   DartType visitBlock(Block node) {
     return analyze(node.statements);
   }
@@ -1170,10 +1176,6 @@ class TypeCheckerVisitor extends Visitor<DartType> {
   }
 
   DartType visitSend(Send node) {
-    if (elements.isAssert(node)) {
-      return analyzeInvocation(node, const AssertAccess());
-    }
-
     Element element = elements[node];
 
     if (element != null && element.isConstructor) {