Add a parent environment to HEnvironment.

This code has no functionality change. It adds a placeholder
for chaining inlined frames.

Change-Id: I5ec57335af76ee406052345b947aad98a6a4423a
diff --git a/compiler/optimizing/dominator_test.cc b/compiler/optimizing/dominator_test.cc
index 61a7697..78ae1dd 100644
--- a/compiler/optimizing/dominator_test.cc
+++ b/compiler/optimizing/dominator_test.cc
@@ -27,7 +27,7 @@
 static void TestCode(const uint16_t* data, const int* blocks, size_t blocks_length) {
   ArenaPool pool;
   ArenaAllocator allocator(&pool);
-  HGraph* graph = new (&allocator) HGraph(&allocator);
+  HGraph* graph = CreateGraph(&allocator);
   HGraphBuilder builder(graph);
   const DexFile::CodeItem* item = reinterpret_cast<const DexFile::CodeItem*>(data);
   bool graph_built = builder.BuildGraph(*item);