[wasm] Implement importing of WebAssembly.Memory.

src/wasm/wasm-js.cc

 // Copyright 2015 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.
 
 #include "src/api-natives.h"
 #include "src/api.h"
 #include "src/asmjs/asm-js.h"
 #include "src/asmjs/asm-typer.h"
 #include "src/asmjs/asm-wasm-builder.h"
 #include "src/assert-scope.h"
@@ skipping 719 matching lines @@
                                             &in_object_properties);
 
     int unused_property_fields = in_object_properties - pre_allocated;
     Handle<Map> map = Map::CopyInitialMap(
         prev_map, instance_size, in_object_properties, unused_property_fields);
 
     context->set_wasm_function_map(*map);
   }
 }
 
+bool WasmJs::IsWasmMemoryObject(Isolate* isolate, Handle<Object> value) {
+  if (value->IsJSObject()) {
+    i::Handle<i::JSObject> object = i::Handle<i::JSObject>::cast(value);
+    i::Handle<i::Symbol> sym(isolate->context()->wasm_memory_sym(), isolate);
+    Maybe<bool> has_brand = i::JSObject::HasOwnProperty(object, sym);

[ahaas, 2016/10/07 08:23:36]

Can sym also be further up the prototype chain? If yes, I think you should not
use HasOwnProperty but JSReceiver::HasProperty.

[titzer, 2016/10/07 08:50:52]

Definitely don't want to go up the prototype chain. I copied a bit of code from
the BrandCheck() above.

+    if (has_brand.IsNothing()) return false;
+    if (has_brand.ToChecked()) return true;
+  }
+  return false;
+}
+
+Handle<JSArrayBuffer> WasmJs::GetWasmMemoryArrayBuffer(Isolate* isolate,
+                                                       Handle<Object> value) {
+  DCHECK(IsWasmMemoryObject(isolate, value));
+  Handle<Object> buf(JSObject::cast(*value)->GetInternalField(0), isolate);

[ahaas, 2016/10/07 08:23:36]

Could we use a constant for index 0?

[titzer, 2016/10/07 08:50:52]

Done.

+  return Handle<JSArrayBuffer>::cast(buf);
+}
 }  // namespace internal
 }  // namespace v8