Move Assemblers to the Arena.

And clean up some APIs to return std::unique_ptr<> instead
of raw pointers that don't communicate ownership.

Change-Id: I3017302307a0253d661240750298802fb0d9585e
diff --git a/runtime/base/arena_allocator.cc b/runtime/base/arena_allocator.cc
index 70ff60f..d951089 100644
--- a/runtime/base/arena_allocator.cc
+++ b/runtime/base/arena_allocator.cc
@@ -77,9 +77,11 @@
   "RegAllocVldt ",
   "StackMapStm  ",
   "CodeGen      ",
+  "Assembler    ",
   "ParallelMove ",
   "GraphChecker ",
   "Verifier     ",
+  "CallingConv  ",
 };
 
 template <bool kCount>