[heap] Use atomic length accessors in body descriptors.

BUG=chromium:694255

Change-Id: I87bfe8eee853ece1260ffc34b61213720ef3e5fa
Reviewed-on: https://chromium-review.googlesource.com/531008
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45895}

src/objects-body-descriptors-inl.h

@@ -284,7 +284,7 @@ class ByteArray::BodyDescriptor final : public BodyDescriptorBase {
   static inline void IterateBody(HeapObject* obj, int object_size) {}
 
   static inline int SizeOf(Map* map, HeapObject* obj) {
-    return reinterpret_cast<ByteArray*>(obj)->ByteArraySize();
+    return ByteArray::SizeFor(ByteArray::cast(obj)->synchronized_length());
   }
 };
 
@@ -312,7 +312,8 @@ class BytecodeArray::BodyDescriptor final : public BodyDescriptorBase {
   }
 
   static inline int SizeOf(Map* map, HeapObject* obj) {
-    return reinterpret_cast<BytecodeArray*>(obj)->BytecodeArraySize();
+    return BytecodeArray::SizeFor(
+        BytecodeArray::cast(obj)->synchronized_length());
   }
 };
 
@@ -329,7 +330,7 @@ class FixedDoubleArray::BodyDescriptor final : public BodyDescriptorBase {
 
   static inline int SizeOf(Map* map, HeapObject* obj) {
     return FixedDoubleArray::SizeFor(
-        reinterpret_cast<FixedDoubleArray*>(obj)->length());
+        FixedDoubleArray::cast(obj)->synchronized_length());
   }
 };
 
@@ -352,7 +353,7 @@ class FixedTypedArrayBase::BodyDescriptor final : public BodyDescriptorBase {
   }
 
   static inline int SizeOf(Map* map, HeapObject* object) {
-    return reinterpret_cast<FixedTypedArrayBase*>(object)->size();
+    return FixedTypedArrayBase::cast(object)->size();
   }
 };