Clean up ScopedArenaAllocatorAdapter.

Make the adapter equality-comparable, define aliases for
containers using the adapter and use those aliases.
Fix DebugStackIndirectTopRefImpl assignment.

Change-Id: I689aa8a93d169f63a659dec5040567d7b1343277
diff --git a/compiler/utils/scoped_arena_allocator.h b/compiler/utils/scoped_arena_allocator.h
index d5b003c..c090062 100644
--- a/compiler/utils/scoped_arena_allocator.h
+++ b/compiler/utils/scoped_arena_allocator.h
@@ -235,8 +235,24 @@
 
   template <typename U>
   friend class ScopedArenaAllocatorAdapter;
+
+  template <typename U>
+  friend bool operator==(const ScopedArenaAllocatorAdapter<U>& lhs,
+                         const ScopedArenaAllocatorAdapter<U>& rhs);
 };
 
+template <typename T>
+inline bool operator==(const ScopedArenaAllocatorAdapter<T>& lhs,
+                       const ScopedArenaAllocatorAdapter<T>& rhs) {
+  return lhs.arena_stack_ == rhs.arena_stack_;
+}
+
+template <typename T>
+inline bool operator!=(const ScopedArenaAllocatorAdapter<T>& lhs,
+                       const ScopedArenaAllocatorAdapter<T>& rhs) {
+  return !(lhs == rhs);
+}
+
 inline ScopedArenaAllocatorAdapter<void> ScopedArenaAllocator::Adapter() {
   return ScopedArenaAllocatorAdapter<void>(this);
 }