Support user generated custom native JS classes.

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

 // Copyright (c) 2013, 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;
 
 /**
  * Support for Custom Elements.
  *
  * The support for custom elements the compiler builds a table that maps the
@@ skipping 53 matching lines @@
   }
 
   CustomElementsAnalysisJoin joinFor(Enqueuer enqueuer) =>
       enqueuer.isResolutionQueue ? resolutionJoin : codegenJoin;
 
   void registerInstantiatedClass(ClassElement classElement, Enqueuer enqueuer) {
     classElement.ensureResolved(compiler.resolution);
     if (!Elements.isNativeOrExtendsNative(classElement)) return;
     if (classElement.isMixinApplication) return;
     if (classElement.isAbstract) return;
+    if (classElement.isJsInterop) return;
     joinFor(enqueuer).instantiatedClasses.add(classElement);
   }
 
   void registerTypeLiteral(DartType type, Registry registry) {
     assert(registry.isForResolution);
     // In codegen we see the TypeConstants instead.
     if (!registry.isForResolution) return;
 
     if (type.isInterfaceType) {
       // TODO(sra): If we had a flow query from the type literal expression to
@@ skipping 60 matching lines @@
   // ClassesOutput: classes requiring metadata.
   final activeClasses = new Set<ClassElement>();
 
   CustomElementsAnalysisJoin(this.backend);
 
   void flush(Enqueuer enqueuer) {
     if (!demanded) return;
     var newActiveClasses = new Set<ClassElement>();
     for (ClassElement classElement in instantiatedClasses) {
       bool isNative = classElement.isNative;
+      // JsInterop classes are opaque interfaces without a concrete
+      // implementation.
+      if (classElement.isJsInterop) continue;

[Siggi Cherem (dart-lang), 2015/10/06 22:38:02]

can this happen given the change you have above in line 74?

[Jacob, 2015/10/13 01:19:23]

nope. Removed and moved comment to the other isJsInterop case

       bool isExtension =
           !isNative && Elements.isNativeOrExtendsNative(classElement);
       // Generate table entries for native classes that are explicitly named and
       // extensions that fix our criteria.
       if ((isNative && selectedClasses.contains(classElement)) ||
           (isExtension &&
               (allClassesSelected || selectedClasses.contains(classElement)))) {
         newActiveClasses.add(classElement);
         Iterable<Element> escapingConstructors =
             computeEscapingConstructors(classElement);
@@ skipping 33 matching lines @@
           result.add(member);
         }
       }
     }
     classElement.forEachMember(selectGenerativeConstructors,
         includeBackendMembers: false,
         includeSuperAndInjectedMembers: false);
     return result;
   }
 }