Fix C++ type of Factory::NewFixedDoubleArray.

src/factory.h

Index: src/factory.h
diff --git a/src/factory.h b/src/factory.h
index f29aac4aa8fee8dd43d48712bf562040e44f0f6a..c086b51ccb43e3c1cc75058f5d499f7b2740dcf3 100644
--- a/src/factory.h
+++ b/src/factory.h
@@ -33,12 +33,14 @@ class Factory V8_FINAL {
   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);