Fix JS-backend when MirrorsUsed target a static field, but there is no mirrors usage.

sdk/lib/_internal/compiler/implementation/enqueue.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 dart2js;
 
 typedef ItemCompilationContext ItemCompilationContextCreator();
 
 class EnqueueTask extends CompilerTask {
   final ResolutionEnqueuer resolution;
@@ skipping 67 matching lines @@
       = new Map<String, Link<Element>>();
   final Map<String, Link<Element>> instanceFunctionsByName
       = new Map<String, Link<Element>>();
   final Set<ClassElement> seenClasses = new Set<ClassElement>();
   final Universe universe = new Universe();
 
   bool queueIsClosed = false;
   EnqueueTask task;
   native.NativeEnqueuer nativeEnqueuer;  // Set by EnqueueTask
 
-  bool hasEnqueuedEverything = false;
+  bool hasEnqueuedReflectiveElements = false;
 
   Enqueuer(this.name, this.compiler, this.itemCompilationContextCreator);
 
   Queue<WorkItem> get queue;
 
   /// Returns [:true:] if this enqueuer is the resolution enqueuer.
   bool get isResolutionQueue => false;
 
   /// Returns [:true:] if [member] has been processed by this enqueuer.
   bool isProcessed(Element member);
@@ skipping 253 matching lines @@
       }
     }
   }
 
   /// Called when [:new Symbol(...):] is seen.
   void registerNewSymbol(TreeElements elements) {
     compiler.backend.registerNewSymbol(elements);
   }
 
   void enqueueEverything() {
-    if (hasEnqueuedEverything) return;
+    if (hasEnqueuedReflectiveElements) return;
     compiler.log('Enqueuing everything');
     task.ensureAllElementsByName();
     for (Link link in task.allElementsByName.values) {
       for (Element element in link) {
         pretendElementWasUsed(element, compiler.globalDependencies);
       }
     }
-    hasEnqueuedEverything = true;
+    hasEnqueuedReflectiveElements = true;
+  }
+
+  /// Enqueue the static fields that have been marked as used by reflective
+  /// usage through `MirrorsUsed`.
+  void enqueueReflectiveStaticFields(Iterable<Element> elements) {
+    if (hasEnqueuedReflectiveElements) return;
+    hasEnqueuedReflectiveElements = true;
+    for (Element element in elements) {
+      pretendElementWasUsed(element, compiler.globalDependencies);
+    }
   }
 
   processLink(Map<String, Link<Element>> map,
               String memberName,
               bool f(Element e)) {
     Link<Element> members = map[memberName];
     if (members != null) {
       // [f] might add elements to [: map[memberName] :] during the loop below
       // so we create a new list for [: map[memberName] :] and prepend the
       // [remaining] members after the loop.
@@ skipping 371 matching lines @@
     }
     CodegenWorkItem workItem = new CodegenWorkItem(
         element, itemCompilationContextCreator());
     queue.add(workItem);
   }
 
   void _logSpecificSummary(log(message)) {
     log('Compiled ${generatedCode.length} methods.');
   }
 }