Optimizing: Fix register allocator validation memory usage.

Also attribute ArenaBitVector allocations to appropriate
passes. This was used to track down the source of the
excessive memory alloactions.

Bug: 27690481

Change-Id: Ib895984cb7c04e24cbc7abbd8322079bab8ab100
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index d64a786..32869ec 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -856,7 +856,8 @@
     uint32_t register_mask = 0;   // Not used.
 
     // The stack mask is not used, so we leave it empty.
-    ArenaBitVector* stack_mask = new (arena) ArenaBitVector(arena, 0, /* expandable */ true);
+    ArenaBitVector* stack_mask =
+        ArenaBitVector::Create(arena, 0, /* expandable */ true, kArenaAllocCodeGenerator);
 
     stack_map_stream_.BeginStackMapEntry(dex_pc,
                                          native_pc,