Check that environments assigned via AssignEnvironment are actually used.

src/lithium.h

Index: src/lithium.h
diff --git a/src/lithium.h b/src/lithium.h
index 8ae5b879dc7bbe6b6f53388b8efec5011d1a89d0..161da8f0a3b6e8ecc0ee8f3cf36add6103db63a1 100644
--- a/src/lithium.h
+++ b/src/lithium.h
@@ -426,7 +426,8 @@ class LEnvironment V8_FINAL : public ZoneObject {
         object_mapping_(0, zone),
         outer_(outer),
         entry_(entry),
-        zone_(zone) { }
+        zone_(zone),
+        has_been_used_(false) { }
 
   Handle<JSFunction> closure() const { return closure_; }
   FrameType frame_type() const { return frame_type_; }
@@ -442,6 +443,9 @@ class LEnvironment V8_FINAL : public ZoneObject {
   HEnterInlined* entry() { return entry_; }
   Zone* zone() const { return zone_; }
 
+  bool has_been_used() const { return has_been_used_; }
+  void set_has_been_used() { has_been_used_ = true; }
+
   void AddValue(LOperand* operand,
                 Representation representation,
                 bool is_uint32) {
@@ -541,6 +545,7 @@ class LEnvironment V8_FINAL : public ZoneObject {
   LEnvironment* outer_;
   HEnterInlined* entry_;
   Zone* zone_;
+  bool has_been_used_;
 };