dart2js cps: Add SetLength instruction.

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

 // Copyright (c) 2014, 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.
 
 library code_generator;
 
 import 'glue.dart';
 
 import '../../closure.dart' show
     ClosureClassElement;
@@ skipping 1193 matching lines @@
         }
       }
       return null;
     }
 
     int maxBit = maxBitOf(node);
     if (maxBit != null && maxBit <= MAX_UINT31) return op;
     return js.js('# >>> 0', [op]);
   }
 
-
-  /// The JS name of a built-in method.
-  static final Map<BuiltinMethod, String> builtinMethodName =
-    const <BuiltinMethod, String>{
-      BuiltinMethod.Push: 'push',
-      BuiltinMethod.Pop: 'pop',
-  };
-
   @override
   js.Expression visitApplyBuiltinMethod(tree_ir.ApplyBuiltinMethod node) {
-    String name = builtinMethodName[node.method];
     js.Expression receiver = visitExpression(node.receiver);
     List<js.Expression> args = visitExpressionList(node.arguments);
-    return js.js('#.#(#)', [receiver, name, args]);
+    switch (node.method) {
+      case BuiltinMethod.Push:
+        return js.js('#.push(#)', [receiver, args]);
+
+      case BuiltinMethod.Pop:
+        return js.js('#.pop()', [receiver]);
+
+      case BuiltinMethod.SetLength:
+        return js.js('#.length = #', [receiver, args[0]]);
+    }
   }
 
   @override
   js.Expression visitAwait(tree_ir.Await node) {
     return new js.Await(visitExpression(node.input));
   }
 
   /// Ensures that parameter defaults will be emitted.
   ///
   /// Ideally, this should be done when generating the relevant stub methods,
   /// since those are the ones that actually reference the constants, but those
   /// are created by the emitter when it is too late to register new constants.
   ///
   /// For non-static methods, we have no way of knowing if the defaults are
   /// actually used, so we conservatively register them all.
   void registerDefaultParameterValues(ExecutableElement element) {
     if (element is! FunctionElement) return;
     FunctionElement function = element;
     if (function.isStatic) return; // Defaults are inlined at call sites.
     function.functionSignature.forEachOptionalParameter((param) {
       ConstantValue constant = glue.getDefaultParameterValue(param);
       registry.registerCompileTimeConstant(constant);
     });
   }
 }