Make 'where' lazy.

sdk/lib/_internal/compiler/implementation/js_backend/native_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;
 
 class NativeEmitter {
 
   CodeEmitterTask emitter;
   CodeBuffer nativeBuffer;
@@ skipping 278 matching lines @@
       seen.add(cls);
       for (final ClassElement subclass in getDirectSubclasses(cls)) {
         visit(subclass);
       }
       classes.add(cls);
     }
     for (final ClassElement classElement in classesWithDynamicDispatch) {
       visit(classElement);
     }
 
-    Collection<ClassElement> dispatchClasses = classes.where(
+    List<ClassElement> dispatchClasses = classes.where(
         (cls) => !getDirectSubclasses(cls).isEmpty &&
-                  classesWithDynamicDispatch.contains(cls));
+                  classesWithDynamicDispatch.contains(cls)).toList();
 
     nativeBuffer.add('// ${classes.length} classes\n');
-    Collection<ClassElement> classesThatHaveSubclasses = classes.where(
+    Iterable<ClassElement> classesThatHaveSubclasses = classes.where(
         (ClassElement t) => !getDirectSubclasses(t).isEmpty);
     nativeBuffer.add('// ${classesThatHaveSubclasses.length} !leaf\n');
 
     // Generate code that builds the map from cls tags used in dynamic dispatch
     // to the set of cls tags of classes that extend (TODO: or implement) those
     // classes.  The set is represented as a string of tags joined with '|'.
     // This is easily split into an array of tags, or converted into a regexp.
     //
     // To reduce the size of the sets, subsets are CSE-ed out into variables.
     // The sets could be much smaller if we could make assumptions about the
@@ skipping 160 matching lines @@
         if (!first) targetBuffer.add(",\n");
         targetBuffer.add(" $name: $function");
         first = false;
       });
       targetBuffer.add("\n});\n\n");
     }
     targetBuffer.add(nativeBuffer);
     targetBuffer.add('\n');
   }
 }