Optimizing: Tag arena allocations in SsaBuilder.

Replace GrowableArray with ArenaVector in SsaBuilder and
tag allocations with a new arena allocation type.

Change-Id: I27312c51d7be9d2ad02a974cce93b365c65c5fc4
diff --git a/runtime/base/arena_allocator.cc b/runtime/base/arena_allocator.cc
index 337df38..4e51f55 100644
--- a/runtime/base/arena_allocator.cc
+++ b/runtime/base/arena_allocator.cc
@@ -74,6 +74,7 @@
   "Environment  ",
   "EnvVRegs     ",
   "EnvLocations ",
+  "SsaBuilder   ",
   "MoveOperands ",
   "CodeBuffer   ",
   "StackMaps    ",