[builtins] Get rid of a few %_ClassOf uses.

src/runtime/runtime-typedarray.cc

Index: src/runtime/runtime-typedarray.cc
diff --git a/src/runtime/runtime-typedarray.cc b/src/runtime/runtime-typedarray.cc
index f39e37072d16202254efae172fc6b5a24b1e7111..753cf97f9f5f113f662ba7a4d08a35709abeedbd 100644
--- a/src/runtime/runtime-typedarray.cc
+++ b/src/runtime/runtime-typedarray.cc
@@ -433,6 +433,19 @@ RUNTIME_FUNCTION(Runtime_IsSharedIntegerTypedArray) {
 }
 
 
+RUNTIME_FUNCTION(Runtime_IsSharedInteger32TypedArray) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 1);
+  if (!args[0]->IsJSTypedArray()) {
+    return isolate->heap()->false_value();
+  }
+
+  Handle<JSTypedArray> obj(JSTypedArray::cast(args[0]));
+  return isolate->heap()->ToBoolean(obj->GetBuffer()->is_shared() &&
+                                    obj->type() == kExternalInt32Array);
+}
+
+
 RUNTIME_FUNCTION(Runtime_DataViewInitialize) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 4);