Fix bad use of OffsetFrom that fails on ARM (sizeof(Object) wasn't 1).

src/heap-inl.h

Index: src/heap-inl.h
diff --git a/src/heap-inl.h b/src/heap-inl.h
index 1acdb2a081be9e6196ac99c991c7a0fa0aa3fee0..5349be7ab6d9d753254e31442e8614fc40727727 100644
--- a/src/heap-inl.h
+++ b/src/heap-inl.h
@@ -133,7 +133,8 @@ Object* Heap::AllocateRawMap() {
 #ifdef DEBUG
   if (!result->IsFailure()) {
     // Maps have their own alignment.
-    CHECK((OffsetFrom(result) & kMapAlignmentMask) == kHeapObjectTag);
+    CHECK_EQ(static_cast<intptr_t>(kHeapObjectTag),
+             reinterpret_cast<intptr_t>(result) & kMapAlignmentMask);
   }
 #endif
   return result;