[turbofan] remove some of the dependency of Instruction on Schedule

src/zone-containers.h

Index: src/zone-containers.h
diff --git a/src/zone-containers.h b/src/zone-containers.h
index 2ee178029ff8d95c245e02d478d297b09d3f39bb..4998cbf3fe990b08208e93da5a49491d96ee5064 100644
--- a/src/zone-containers.h
+++ b/src/zone-containers.h
@@ -24,6 +24,12 @@ class ZoneVector : public std::vector<T, zone_allocator<T> > {
       : std::vector<T, zone_allocator<T> >(zone_allocator<T>(zone)) {}
 
   // Constructs a new vector and fills it with {size} elements, each
+  // constructed via the default constructor.
+  ZoneVector(int size, Zone* zone)
+      : std::vector<T, zone_allocator<T> >(size, T(), zone_allocator<T>(zone)) {
+  }
+
+  // Constructs a new vector and fills it with {size} elements, each
   // having the value {def}.
   ZoneVector(int size, T def, Zone* zone)
       : std::vector<T, zone_allocator<T> >(size, def, zone_allocator<T>(zone)) {