Fix C++ type of Factory::NewFixedDoubleArray.

src/factory.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_FACTORY_H_
 #define V8_FACTORY_H_
 
 #include "isolate.h"
 
 namespace v8 {
@@ skipping 15 matching lines @@
 
   // Allocate a new fixed array with non-existing entries (the hole).
   Handle<FixedArray> NewFixedArrayWithHoles(
       int size,
       PretenureFlag pretenure = NOT_TENURED);
 
   // Allocates an uninitialized fixed array. It must be filled by the caller.
   Handle<FixedArray> NewUninitializedFixedArray(int size);
 
   // Allocate a new uninitialized fixed double array.
-  Handle<FixedDoubleArray> NewFixedDoubleArray(
+  // The function returns a pre-allocated empty fixed array for capacity = 0,
+  // so the return type must be the general fixed array class.
+  Handle<FixedArrayBase> NewFixedDoubleArray(
       int size,
       PretenureFlag pretenure = NOT_TENURED);
 
   // Allocate a new fixed double array with hole values.
-  Handle<FixedDoubleArray> NewFixedDoubleArrayWithHoles(
+  Handle<FixedArrayBase> NewFixedDoubleArrayWithHoles(
       int size,
       PretenureFlag pretenure = NOT_TENURED);
 
   Handle<ConstantPoolArray> NewConstantPoolArray(
       int number_of_int64_entries,
       int number_of_code_ptr_entries,
       int number_of_heap_ptr_entries,
       int number_of_int32_entries);
 
   Handle<SeededNumberDictionary> NewSeededNumberDictionary(
@@ skipping 629 matching lines @@
   // the string representation of the number.  Otherwise return undefined.
   Handle<Object> GetNumberStringCache(Handle<Object> number);
 
   // Update the cache with a new number-string pair.
   void SetNumberStringCache(Handle<Object> number, Handle<String> string);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_