Restore per-TypedArray-class length accessors as a perf workaround

src/js/typedarray.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function(global, utils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 245 matching lines @@
         NAMEConstructByArrayLike(this, arg1);
       } else {
         NAMEConstructByIterable(this, arg1, iteratorFn);
       }
     }
   } else {
     throw MakeTypeError(kConstructorNotFunction, "NAME")
   }
 }
 
+function NAME_GetLength() {
+  if (!(%_ClassOf(this) === 'NAME')) {
+    throw MakeTypeError(kIncompatibleMethodReceiver, "NAME.length", this);
+  }
+  return %_TypedArrayGetLength(this);
+}
+
 function NAMESubArray(begin, end) {
   var beginInt = TO_INTEGER(begin);
   if (!IS_UNDEFINED(end)) {
     var endInt = TO_INTEGER(end);
     var srcLength = %_TypedArrayGetLength(this);
   } else {
     var srcLength = %_TypedArrayGetLength(this);
     var endInt = srcLength;
   }
 
@@ skipping 546 matching lines @@
   %InternalSetPrototype(GlobalNAME.prototype, TypedArray.prototype);
 
   %AddNamedProperty(GlobalNAME, "BYTES_PER_ELEMENT", ELEMENT_SIZE,
                     READ_ONLY | DONT_ENUM | DONT_DELETE);
 
   %AddNamedProperty(GlobalNAME.prototype,
                     "constructor", global.NAME, DONT_ENUM);
   %AddNamedProperty(GlobalNAME.prototype,
                     "BYTES_PER_ELEMENT", ELEMENT_SIZE,
                     READ_ONLY | DONT_ENUM | DONT_DELETE);
+  utils.InstallGetter(GlobalNAME.prototype, "length", NAME_GetLength,

[adamk, 2016/01/25 19:21:22]

Please add a comment here too.

+                      DONT_ENUM | DONT_DELETE);
 endmacro
 
 TYPED_ARRAYS(SETUP_TYPED_ARRAY)
 
 // --------------------------- DataView -----------------------------
 
 function DataViewConstructor(buffer, byteOffset, byteLength) { // length = 3
   if (IS_UNDEFINED(new.target)) {
     throw MakeTypeError(kConstructorNotFunction, "DataView");
   }
@@ skipping 118 matching lines @@
   "setUint32", DataViewSetUint32JS,
 
   "getFloat32", DataViewGetFloat32JS,
   "setFloat32", DataViewSetFloat32JS,
 
   "getFloat64", DataViewGetFloat64JS,
   "setFloat64", DataViewSetFloat64JS
 ]);
 
 })