deps: cherry-pick 6da51b4 from v8's upstream

Original commit message:
TypedArray accessor detection: consider entire prototype chain
When looking up a special accessor for known TypedArray fields
("length", "byteLength", "byteOffset"), consider the entire
prototype chain, not only the direct prototype.
This allows subclasses of TypedArrays to benefit from fast
specialized accesses.
Review URL: https://codereview.chromium.org/1313493005
Cr-Commit-Position: refs/heads/master@{#30678}
Benchmark results:
buffers/buffer-iterate.js size=16386 type=slow method=for n=1000:
./node: 71607 node: 8702.3 ............ 722.85%
Improvement depends on the code, but generally brings us back to the
performance that we had before the v8 update (if not making it
faster).
Fixes: #2463
PR-URL: #2801
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

Author: indutny

deps/v8/src/accessors.cc

@@ -100,22 +100,37 @@ bool Accessors::IsJSArrayBufferViewFieldAccessor(Handle<Map> map,
  Isolate* isolate = name->GetIsolate();
 
 switch (map->instance_type()) {
-caseJS_TYPED_ARRAY_TYPE:
-// %TypedArray%.prototype is non-configurable, and so are the following
-// named properties on %TypedArray%.prototype, so we can directly inline
-// the field-load for typed array maps that still use their
-// %TypedArray%.prototype.
-if (JSFunction::cast(map->GetConstructor())->prototype() !=
-map->prototype()) {
+caseJS_TYPED_ARRAY_TYPE: {
+if (!CheckForName(name, isolate->factory()->length_string(),
+ JSTypedArray::kLengthOffset, object_offset) &&
+ !CheckForName(name, isolate->factory()->byte_length_string(),
+ JSTypedArray::kByteLengthOffset, object_offset) &&
+ !CheckForName(name, isolate->factory()->byte_offset_string(),
+ JSTypedArray::kByteOffsetOffset, object_offset)) {
 returnfalse;
  }
-returnCheckForName(name, isolate->factory()->length_string(),
- JSTypedArray::kLengthOffset, object_offset) ||
-CheckForName(name, isolate->factory()->byte_length_string(),
- JSTypedArray::kByteLengthOffset, object_offset) ||
-CheckForName(name, isolate->factory()->byte_offset_string(),
- JSTypedArray::kByteOffsetOffset, object_offset);
 
+if (map->is_dictionary_map()) returnfalse;
+
+// Check if the property is overridden on the instance.
+ DescriptorArray* descriptors = map->instance_descriptors();
+int descriptor = descriptors->SearchWithCache(*name, *map);
+if (descriptor != DescriptorArray::kNotFound) returnfalse;
+
+ Handle<Object> proto = Handle<Object>(map->prototype(), isolate);
+if (!proto->IsJSReceiver()) returnfalse;
+
+// Check if the property is defined in the prototype chain.
+ LookupIterator it(proto, name);
+if (!it.IsFound()) returnfalse;
+
+ Object* original_proto =
+JSFunction::cast(map->GetConstructor())->prototype();
+
+// Property is not configurable. It is enough to verify that
+// the holder is the same.
+return *it.GetHolder<Object>() == original_proto;
+ }
 caseJS_DATA_VIEW_TYPE:
 returnCheckForName(name, isolate->factory()->byte_length_string(),
  JSDataView::kByteLengthOffset, object_offset) ||

deps/v8/test/mjsunit/regress/regress-typedarray-length.js

@@ -71,6 +71,43 @@ assertEquals(undefined, get(a));
 assertEquals(undefined,get(a));
 })();
 
+(function(){
+"use strict";
+
+classMyTypedArrayextendsInt32Array{
+constructor(length){
+super(length);
+}
+}
+
+a=newMyTypedArray(1024);
+
+get=function(a){
+returna.length;
+}
+
+assertEquals(1024,get(a));
+assertEquals(1024,get(a));
+assertEquals(1024,get(a));
+%OptimizeFunctionOnNextCall(get);
+assertEquals(1024,get(a));
+})();
+
+(function(){
+"use strict";
+vara=newUint8Array(4);
+Object.defineProperty(a,"length",{get: function(){return"blah";}});
+get=function(a){
+returna.length;
+}
+
+assertEquals("blah",get(a));
+assertEquals("blah",get(a));
+assertEquals("blah",get(a));
+%OptimizeFunctionOnNextCall(get);
+assertEquals("blah",get(a));
+})();
+
 // Ensure we cannot delete length, byteOffset, byteLength.
 assertTrue(Int32Array.prototype.hasOwnProperty("length"));
 assertTrue(Int32Array.prototype.hasOwnProperty("byteOffset"));