Add phase zone to CompilationInfo and use it in GVN pass.

src/hydrogen-gvn.h

Index: src/hydrogen-gvn.h
diff --git a/src/hydrogen-gvn.h b/src/hydrogen-gvn.h
index c39765a1eea32c4c8e23985726a31e0c12dadaea..2d6075e7157a8d558a8d9f496e1e7c6b9e648c8d 100644
--- a/src/hydrogen-gvn.h
+++ b/src/hydrogen-gvn.h
@@ -100,12 +100,15 @@ class HGlobalValueNumberer BASE_EMBEDDED {
 
   HGraph* graph() { return graph_; }
   CompilationInfo* info() { return info_; }
-  Zone* zone() const { return graph_->zone(); }
+  Zone* phase_zone() const { return info_->phase_zone(); }
 
   HGraph* graph_;
   CompilationInfo* info_;
   bool removed_side_effects_;
 
+  Zone* phase_zone_;
+  ZoneScope phase_zone_scope_;
+
   // A map of block IDs to their side effects.
   ZoneList<GVNFlagSet> block_side_effects_;