[wasm] Use more precise types for some WASM objects.

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 517 matching lines @@
     isolate->ThrowException(e);
     return;
   }
 
   uint32_t delta = args[0]->Uint32Value(context).FromJust();
   i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
   i::Handle<i::JSObject> receiver =
       i::Handle<i::JSObject>::cast(Utils::OpenHandle(*args.This()));
   i::Handle<i::Object> instance_object(
       receiver->GetInternalField(kWasmMemoryInstanceObject), i_isolate);
-  i::Handle<i::JSObject> instance(
-      i::Handle<i::JSObject>::cast(instance_object));
+  i::Handle<i::WasmInstanceObject> instance(
+      i::Handle<i::WasmInstanceObject>::cast(instance_object));
 
   // TODO(gdeepti) Implement growing memory when shared by different
   // instances.
   int32_t ret = internal::wasm::GrowInstanceMemory(i_isolate, instance, delta);
   if (ret == -1) {
     v8::Local<v8::Value> e = v8::Exception::Error(
         v8_str(isolate, "Unable to grow instance memory."));
     isolate->ThrowException(e);
     return;
   }
@@ skipping 231 matching lines @@
   i::Handle<i::Symbol> symbol(isolate->context()->wasm_memory_sym(), isolate);
   return HasBrand(value, symbol);
 }
 
 bool WasmJs::IsWasmTableObject(Isolate* isolate, Handle<Object> value) {
   i::Handle<i::Symbol> symbol(isolate->context()->wasm_table_sym(), isolate);
   return HasBrand(value, symbol);
 }
 }  // namespace internal
 }  // namespace v8