Tweak liveness when instructions are used in environments.

Instructions remain live when debuggable, but only instructions
with object types remain live when non-debuggable.

Enable StackVisitor::GetThisObject for optimizing.

Change-Id: Id87b2cbf33a02450059acc9993995782e5f28987
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index ed3f949..38fb051 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -695,6 +695,11 @@
         break;
       }
 
+      case Location::kInvalid: {
+        stack_map_stream_.AddDexRegisterEntry(DexRegisterMap::kNone, 0);
+        break;
+      }
+
       default:
         LOG(FATAL) << "Unexpected kind " << location.GetKind();
     }