Do not evaluate on-demand to prevent breaking the deferred loading task

pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart

Index: pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart
diff --git a/pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart b/pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart
index 23836625b66880663aed375abf8a8cfb25a6aeb1..47fb663270d6d070d9e8d04eec3bb545ca23c081 100644
--- a/pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart
+++ b/pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart
@@ -249,7 +249,9 @@ class JavaScriptConstantCompiler extends ConstantCompilerBase
   ConstantValue getConstantValue(ConstantExpression expression) {
     assert(invariant(CURRENT_ELEMENT_SPANNABLE, expression != null,
         message: "ConstantExpression is null in getConstantValue."));
-    evaluate(expression);
+    // TODO(johhniwinther): ensure expressions have been evaluated at this
+    // point. This can't be enabled today due to dartbug.com/26406.
+
     ConstantValue value = super.getConstantValue(expression);
     if (value == null &&
         expression != null &&