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/nodes.h b/compiler/optimizing/nodes.h
index 46377ee..6736319 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -645,7 +645,7 @@
         irreducible_(false),
         back_edges_(graph->GetArena()->Adapter(kArenaAllocLoopInfoBackEdges)),
         // Make bit vector growable, as the number of blocks may change.
-        blocks_(graph->GetArena(), graph->GetBlocks().size(), true) {
+        blocks_(graph->GetArena(), graph->GetBlocks().size(), true, kArenaAllocLoopInfoBackEdges) {
     back_edges_.reserve(kDefaultNumberOfBackEdges);
   }