message: Add clarity to "Op Name" for device memory allocation that was preallocated and unused.
diff: @@ -320,10 +320,10 @@ void InsertSpecialAllocations(int64 unmapped_allocation_bytes, int64 step_id,
  if (unmapped_allocation_bytes > 0) {
  MemoryActivityMetadata* special_allocation =
  memory_profile->add_special_allocations();
  - FillActivityMetadata(
  - HostEventType::kMemoryAllocation,
  - {unmapped_allocation_bytes, unmapped_allocation_bytes, 0,
  - "preallocated/unknown", step_id, "persist/dynamic", 0, "unknown"},
  + FillActivityMetadata(HostEventType::kMemoryAllocation,
  + {unmapped_allocation_bytes, unmapped_allocation_bytes,
  + 0, "unused preallocated device memory", step_id,
  + "persist/dynamic", 0, "unknown"},
  special_allocation);
  active_allocs->push_back({--index, special_allocation});
  }
  