Fix TPH heap code

1. Fix typo introduced in prior commit.
2. Guard code so TPH does not attempt to use OffThreadSpace.

Bug: v8:9533
Change-Id: I37eeff6a9c6ec4a7c479161a01345aa82c884e54
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2047046Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Steve Blackburn <steveblackburn@google.com>
Cr-Commit-Position: refs/heads/master@{#66214}

src/execution/isolate-utils-inl.h

@@ -27,7 +27,7 @@ V8_INLINE Heap* GetHeapFromWritableObject(HeapObject object) {
   // able to get the heap, but not the isolate, for off-thread objects.
 
 #if defined V8_ENABLE_THIRD_PARTY_HEAP
-  return Heap::GetIsolateFromWritableObject(obj)->heap();
+  return Heap::GetIsolateFromWritableObject(object)->heap();
 #elif defined V8_COMPRESS_POINTERS
   Isolate* isolate = Isolate::FromRoot(GetIsolateRoot(object.ptr()));
   DCHECK_NOT_NULL(isolate);

src/heap/heap.cc

@@ -2958,6 +2958,9 @@ bool Heap::CanMoveObjectStart(HeapObject object) {
 
 // static
 bool Heap::InOffThreadSpace(HeapObject heap_object) {
+#ifdef V8_ENABLE_THIRD_PARTY_HEAP
+  return false;  // currently unsupported
+#else
   Space* owner = MemoryChunk::FromHeapObject(heap_object)->owner();
   if (owner->identity() == OLD_SPACE) {
     // TODO(leszeks): Should we exclude compaction spaces here?
@@ -2967,6 +2970,7 @@ bool Heap::InOffThreadSpace(HeapObject heap_object) {
     return static_cast<LargeObjectSpace*>(owner)->is_off_thread();
   }
   return false;
+#endif
 }
 
 bool Heap::IsImmovable(HeapObject object) {