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

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 1457 matching lines @@
       return const WorldImpact();
     }
     if (element.isConstructor &&
         element.enclosingClass == helpers.jsNullClass) {
       // Work around a problem compiling JSNull's constructor.
       return const CodegenImpact();
     }
     if (kind.category == ElementCategory.VARIABLE) {
       VariableElement variableElement = element;
       ConstantExpression constant = variableElement.constant;
-      if (constant != null) {
-        ConstantValue initialValue = constants.getConstantValue(constant);
+      // TODO(johnniwinther): ensure `initialValue` is not null. Note that
+      // calling `evaluate` in getConstantValue may trigger issues for deferred
+      // loading (dartbug.com/26406).
+      ConstantValue initialValue =
+          constant == null ? null : constants.getConstantValue(constant);
+      if (initialValue != null) {
         registerCompileTimeConstant(initialValue, work.registry);
         addCompileTimeConstantForEmission(initialValue);
         // We don't need to generate code for static or top-level
         // variables. For instance variables, we may need to generate
         // the checked setter.
         if (Elements.isStaticOrTopLevel(element)) {
           return impactTransformer
               .transformCodegenImpact(work.registry.worldImpact);
         }
       } else {
@@ skipping 1553 matching lines @@
 
   @override
   void onImpactUsed(ImpactUseCase impactUse) {
     if (impactUse == DeferredLoadTask.IMPACT_USE && !supportSerialization) {
       // TODO(johnniwinther): Allow emptying when serialization has been
       // performed.
       resolution.emptyCache();
     }
   }
 }