Use heapAlignSize in newAlloc

Summary:
The `size` parameter passed to these two functions is not the actual final
size in the heap, as the heap may round the size up if it isn't a multiple of
`HeapAlign` (which happens to be 8).

This was a quite rare occurrence, since most of our objects happen to have
a size that is a multiple of 8 anyway; however, it can happen, and if it did,
`freeAlloc` would try to subtract more bytes than were added, resulting in an assert.

Reviewed By: neildhar

Differential Revision: D25078476

fbshipit-source-id: cc7c0c824f3d41fe3ddc8ec6a7a1d34b96d896f0

include/hermes/VM/Runtime.h

@@ -1652,7 +1652,7 @@ T *Runtime::makeAFixed(Args &&... args) {
   T *ptr = heap_.makeA<T, true /* fixedSize */, hasFinalizer, longLived>(
       sz, std::forward<Args>(args)...);
 #ifdef HERMES_ENABLE_ALLOCATION_LOCATION_TRACES
-  heap_.getAllocationLocationTracker().newAlloc(ptr, sz);
+  heap_.getAllocationLocationTracker().newAlloc(ptr, heapAlignSize(sz));
 #endif
   return ptr;
 }
@@ -1675,7 +1675,7 @@ T *Runtime::makeAVariable(uint32_t size, Args &&... args) {
   T *ptr = heap_.makeA<T, false /* fixedSize */, hasFinalizer, longLived>(
       size, std::forward<Args>(args)...);
 #ifdef HERMES_ENABLE_ALLOCATION_LOCATION_TRACES
-  heap_.getAllocationLocationTracker().newAlloc(ptr, size);
+  heap_.getAllocationLocationTracker().newAlloc(ptr, heapAlignSize(size));
 #endif
   return ptr;
 }