Update dart2js unit tests to new library API.

dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.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;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 1390 matching lines @@
       extraArg = 'receiver';
     } else {
       cache = boundClosureCache;
     }
     List<String> fieldNames = compiler.enableMinification
         ? inInterceptor ? const ['a', 'b', 'c']
                         : const ['a', 'b']
         : inInterceptor ? const ['self', 'target', 'receiver']
                         : const ['self', 'target'];
 
-    Collection<Element> typedefChecks =
+    Iterable<Element> typedefChecks =
         getTypedefChecksOn(member.computeType(compiler));
     bool hasTypedefChecks = !typedefChecks.isEmpty;
 
     bool canBeShared = !hasOptionalParameters && !hasTypedefChecks;
 
     String closureClass = canBeShared ? cache[parameterCount] : null;
     if (closureClass == null) {
       // Either the class was not cached yet, or there are optional parameters.
       // Create a new closure class.
       SourceString name = const SourceString("BoundClosure");
@@ skipping 660 matching lines @@
     if (backend.objectInterceptorClass == null) return;
     String objectName = namer.isolateAccess(backend.objectInterceptorClass);
     backend.specializedGetInterceptors.forEach(
         (String key, Collection<ClassElement> classes) {
           emitGetInterceptorMethod(buffer, objectName, key, classes);
         });
   }
 
   void computeNeededClasses() {
     instantiatedClasses =
-        compiler.codegenWorld.instantiatedClasses.where(computeClassFilter());
+        compiler.codegenWorld.instantiatedClasses.where(computeClassFilter())
+            .toSet();
     neededClasses = instantiatedClasses.toSet();
     for (ClassElement element in instantiatedClasses) {
       for (ClassElement superclass = element.superclass;
           superclass != null;
           superclass = superclass.superclass) {
         if (neededClasses.contains(superclass)) break;
         neededClasses.add(superclass);
       }
     }
   }
@@ skipping 79 matching lines @@
 """;
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;