Introduce a new AccessorPair type for handling JavaScript accessors.

src/profile-generator.cc

Index: src/profile-generator.cc
diff --git a/src/profile-generator.cc b/src/profile-generator.cc
index 00fc7b736a7c5f5e4798cf2e32129cd79a5676e7..2252c69717a28b331a15012cc09fd88eb6237f54 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -2226,13 +2226,13 @@ void V8HeapExplorer::ExtractPropertyReferences(JSObject* js_obj,
           break;
         case CALLBACKS: {
           Object* callback_obj = descs->GetValue(i);
-          if (callback_obj->IsFixedArray()) {
-            FixedArray* accessors = FixedArray::cast(callback_obj);
-            if (Object* getter = accessors->get(JSObject::kGetterIndex)) {
+          if (callback_obj->IsAccessorPair()) {
+            AccessorPair* accessors = AccessorPair::cast(callback_obj);
+            if (Object* getter = accessors->getter()) {
               SetPropertyReference(js_obj, entry, descs->GetKey(i),
                                    getter, "get-%s");
             }
-            if (Object* setter = accessors->get(JSObject::kSetterIndex)) {
+            if (Object* setter = accessors->setter()) {
               SetPropertyReference(js_obj, entry, descs->GetKey(i),
                                    setter, "set-%s");
             }