dart2js: --fast-startup: share defaultValues property for closures with no default values

pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart

 // Copyright (c) 2015, 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.js_emitter.startup_emitter.model_emitter;
 
 /// The name of the property that stores the tear-off getter on a static
 /// function.
 ///
 /// This property is only used when isolates are used.
@@ skipping 698 matching lines @@
       checkedSetters,
       isChecks,
       callStubs,
       noSuchMethodStubs,
       gettersSetters
     ].expand((x) => x);
 
     List<js.Property> properties = <js.Property>[];
 
     if (cls.superclass == null) {
+      // TODO(sra): What is this doing? Document or remove.
       properties
           .add(new js.Property(js.string("constructor"), classReference(cls)));
       properties
           .add(new js.Property(namer.operatorIs(cls.element), js.number(1)));
     }
 
     allMethods.forEach((Method method) {
       emitInstanceMethod(method)
           .forEach((js.Expression name, js.Expression code) {
         var prop = new js.Property(name, code);
         compiler.dumpInfoTask.registerElementAst(method.element, prop);
         properties.add(prop);
       });
     });
 
+    if (cls.isClosureBaseClass) {
+      // Closures extend a common base class, so we can put properties on the
+      // prototype for common values.
+
+      // Most closures have no optional arguments.
+      properties.add(new js.Property(
+          js.string(namer.defaultValuesField), new js.LiteralNull()));
+    }
+
     return new js.ObjectInitializer(properties);
   }
 
   /// Generates a getter for the given [field].
   Method generateGetter(Field field) {
     assert(field.needsGetter);
 
     String template;
     if (field.needsInterceptedGetterOnReceiver) {
       template = "function(receiver) { return receiver[#]; }";
@@ skipping 54 matching lines @@
   Map<js.Expression, js.Expression> emitInstanceMethod(Method method) {
     var properties = <js.Expression, js.Expression>{};
 
     properties[method.name] = method.code;
     if (method is InstanceMethod) {
       for (ParameterStubMethod stubMethod in method.parameterStubs) {
         properties[stubMethod.name] = stubMethod.code;
       }
 
       if (method.isClosureCallMethod && method.canBeApplied) {
+        // TODO(sra): We should also add these properties for the user-defined
+        // `call` method on classes. Function.apply is currently broken for
+        // complex cases. [forceAdd] might be true when this is fixed.
+        bool forceAdd = !method.isClosureCallMethod;
+
         properties[js.string(namer.callCatchAllName)] =
             js.quoteName(method.name);
         properties[js.string(namer.requiredParameterField)] =
             js.number(method.requiredParameterCount);
-        properties[js.string(namer.defaultValuesField)] =
+
+        js.Expression defaultValues =
             _encodeOptionalParameterDefaultValues(method);
+        // Default values property of `null` is stored on the common JS
+        // superclass.
+        if (defaultValues is! js.LiteralNull || forceAdd) {
+          properties[js.string(namer.defaultValuesField)] = defaultValues;
+        }
       }
     }
 
     return properties;
   }
 
   /// Emits the inheritance block of the fragment.
   ///
   /// In this section prototype chains are updated and mixin functions are
   /// copied.
@@ skipping 568 matching lines @@
     }
     statements.add(js.js.statement("setOrUpdateInterceptorsByTag(#);",
         js.objectLiteral(interceptorsByTag)));
     statements.add(
         js.js.statement("setOrUpdateLeafTags(#);", js.objectLiteral(leafTags)));
     statements.addAll(subclassAssignments);
 
     return wrapPhase('nativeSupport', new js.Block(statements));
   }
 }