Enable emplace_back for zone containers

src/zone/zone-allocator.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ZONE_ZONE_ALLOCATOR_H_
 #define V8_ZONE_ZONE_ALLOCATOR_H_
 #include <limits>
 
 #include "src/zone/zone.h"
 
@@ skipping 31 matching lines @@
   pointer allocate(size_type n, const void* hint = 0) {
     return static_cast<pointer>(
         zone_->NewArray<value_type>(static_cast<int>(n)));
   }
   void deallocate(pointer p, size_type) { /* noop for Zones */
   }
 
   size_type max_size() const throw() {
     return std::numeric_limits<int>::max() / sizeof(value_type);
   }
-  void construct(pointer p, const T& val) {
-    new (static_cast<void*>(p)) T(val);
+  template <typename U, typename... Args>
+  void construct(U* p, Args&&... args) {
+    void* v_p = const_cast<void*>(static_cast<const void*>(p));
+    new (v_p) U(std::forward<Args>(args)...);
   }
-  void destroy(pointer p) { p->~T(); }
+  template <typename U>
+  void destroy(U* p) {
+    p->~U();
+  }
 
   bool operator==(zone_allocator const& other) const {
     return zone_ == other.zone_;
   }
   bool operator!=(zone_allocator const& other) const {
     return zone_ != other.zone_;
   }
 
   Zone* zone() { return zone_; }
 
  private:
   Zone* zone_;
 };
 
 typedef zone_allocator<bool> ZoneBoolAllocator;
 typedef zone_allocator<int> ZoneIntAllocator;
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ZONE_ZONE_ALLOCATOR_H_