Introduce {ConstantElementsPair} struct for type safety.

src/ast/compile-time-value.h

 // Copyright 2015 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_AST_COMPILE_TIME_VALUE
 #define V8_AST_COMPILE_TIME_VALUE
 
 #include "src/allocation.h"
 #include "src/globals.h"
 
@@ skipping 13 matching lines @@
   };
 
   static bool IsCompileTimeValue(Expression* expression);
 
   // Get the value as a compile time value.
   static Handle<FixedArray> GetValue(Isolate* isolate, Expression* expression);
 
   // Get the type of a compile time value returned by GetValue().
   static LiteralType GetLiteralType(Handle<FixedArray> value);
 
-  // Get the elements array of a compile time value returned by GetValue().
-  static Handle<FixedArray> GetElements(Handle<FixedArray> value);
+  // Get the elements of a compile time value returned by GetValue().
+  static Handle<HeapObject> GetElements(Handle<FixedArray> value);
 
  private:
   static const int kLiteralTypeSlot = 0;
   static const int kElementsSlot = 1;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_COMPILE_TIME_VALUE