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/nodes.cc b/compiler/optimizing/nodes.cc
index 85c0361..b9e58c7 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -37,8 +37,9 @@
     instruction->RemoveAsUserOfInput(i);
   }
 
-  HEnvironment* environment = instruction->GetEnvironment();
-  if (environment != nullptr) {
+  for (HEnvironment* environment = instruction->GetEnvironment();
+       environment != nullptr;
+       environment = environment->GetParent()) {
     for (size_t i = 0, e = environment->Size(); i < e; ++i) {
       if (environment->GetInstructionAt(i) != nullptr) {
         environment->RemoveAsUserOfInput(i);