Skip spurious constants in deferred computation.

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 47fb663270d6d070d9e8d04eec3bb545ca23c081..5aefd3955ad11fa61c66b385af034a094e388201 100644
--- a/pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart
+++ b/pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart
@@ -26,6 +26,11 @@ class JavaScriptConstantTask extends ConstantCompilerTask {
   ConstantSystem get constantSystem => dartConstantCompiler.constantSystem;
 
   @override
+  bool hasConstantValue(ConstantExpression expression) {
+    return dartConstantCompiler.hasConstantValue(expression);
+  }
+
+  @override
   ConstantValue getConstantValue(ConstantExpression expression) {
     return dartConstantCompiler.getConstantValue(expression);
   }
@@ -251,7 +256,9 @@ class JavaScriptConstantCompiler extends ConstantCompilerBase
         message: "ConstantExpression is null in getConstantValue."));
     // TODO(johhniwinther): ensure expressions have been evaluated at this
     // point. This can't be enabled today due to dartbug.com/26406.
-
+    if (compiler.serialization.supportsDeserialization) {
+      evaluate(expression);
+    }
     ConstantValue value = super.getConstantValue(expression);
     if (value == null &&
         expression != null &&