Revert r1529, which failed on some of the benchmarks.

src/virtual-frame.cc

Index: src/virtual-frame.cc
===================================================================
--- src/virtual-frame.cc	(revision 1531)
+++ src/virtual-frame.cc	(working copy)
@@ -93,11 +93,9 @@
     case FrameElement::REGISTER:
       // All copies are backed by memory or register locations.
       result.type_ =
-          FrameElement::TypeField::encode(FrameElement::COPY)
-          | FrameElement::IsCopiedField::encode(false)
-          | FrameElement::SyncField::encode(FrameElement::NOT_SYNCED);
+          FrameElement::TypeField::encode(FrameElement::COPY) |
+          FrameElement::SyncField::encode(FrameElement::NOT_SYNCED);
       result.data_.index_ = index;
-      elements_[index].set_copied();
       break;
 
     case FrameElement::INVALID:
@@ -369,8 +367,7 @@
 
   // If the original may be a copy, adjust to preserve the copy-on-write
   // semantics of copied elements.
-  if (original.is_copied() &&
-      (original.is_register() || original.is_memory())) {
+  if (original.is_register() || original.is_memory()) {
     FrameElement ignored = AdjustCopies(frame_index);
   }