Print memory usage in dex2oat shutdown

Example on mako:
I/dex2oat (31071): dex2oat took 31.195s (threads: 2) arena alloc=1013KB java alloc=13MB native alloc=32MB free=1490KB

Bug: 18069309

Change-Id: I08eac00842be35d4e659bddc8513f2062be725c9

(cherry picked from commit 3029df6d212894647ba0e5c23443c40912c6ecc8)
diff --git a/compiler/driver/compiler_driver.h b/compiler/driver/compiler_driver.h
index 437a1a9..d837dbc 100644
--- a/compiler/driver/compiler_driver.h
+++ b/compiler/driver/compiler_driver.h
@@ -340,6 +340,9 @@
   ArenaPool* GetArenaPool() {
     return &arena_pool_;
   }
+  const ArenaPool* GetArenaPool() const {
+    return &arena_pool_;
+  }
 
   bool WriteElf(const std::string& android_root,
                 bool is_host,