Introduce and use dwarf_scanner_base

This introduces dwarf_scanner_base, a base class for all the index
readers in the DWARF code.  Then, it changes both mapped_index_base
and cooked_index_vector to derive from this new base class.

gdb/dwarf2/cooked-index.h

@@ -31,6 +31,7 @@
 #include "addrmap.h"
 #include "gdbsupport/iterator-range.h"
 #include "gdbsupport/thread-pool.h"
+#include "dwarf2/mapped-index.h"
 
 struct dwarf2_per_cu_data;
 
@@ -241,7 +242,7 @@ private:
    cooked_index_vector for storage and final indexing.  The index is
    made by iterating over the entries previously created.  */
 
-class cooked_index_vector
+class cooked_index_vector : public dwarf_scanner_base
 {
 public:
 
@@ -291,6 +292,8 @@ public:
      "main".  This will return NULL if no such entry is available.  */
   const cooked_index_entry *get_main () const;
 
+  quick_symbol_functions_up make_quick_functions () const override;
+
 private:
 
   /* GNAT only emits mangled ("encoded") names in the DWARF, and does

gdb/dwarf2/mapped-index.h

@@ -47,13 +47,25 @@ struct name_component
   offset_type idx;
 };
 
+/* Base class of all DWARF scanner types.  */
+
+struct dwarf_scanner_base
+{
+  dwarf_scanner_base () = default;
+  virtual ~dwarf_scanner_base () = default;
+  DISABLE_COPY_AND_ASSIGN (dwarf_scanner_base);
+
+  /* Return a quick_symbol_functions instance that refers back to this
+     dwarf_scanner_base.  */
+  virtual quick_symbol_functions_up make_quick_functions () const = 0;
+};
+
 /* Base class containing bits shared by both .gdb_index and
    .debug_name indexes.  */
 
-struct mapped_index_base
+struct mapped_index_base : public dwarf_scanner_base
 {
   mapped_index_base () = default;
-  virtual ~mapped_index_base() = default;
   DISABLE_COPY_AND_ASSIGN (mapped_index_base);
 
   /* The name_component table (a sorted vector).  See name_component's
@@ -77,10 +89,6 @@ struct mapped_index_base
     return false;
   }
 
-  /* Return a quick_symbol_functions instance that refers back to this
-     mapped_index_base.  */
-  virtual quick_symbol_functions_up make_quick_functions () const = 0;
-
   /* Build the symbol name component sorted vector, if we haven't
      yet.  */
   void build_name_components (dwarf2_per_objfile *per_objfile);

gdb/dwarf2/read.c

@@ -5301,7 +5301,8 @@ dwarf2_initialize_objfile (struct objfile *objfile)
   if (per_bfd->cooked_index_table != nullptr)
     {
       dwarf_read_debug_printf ("re-using cooked index table");
-      objfile->qf.push_front (make_cooked_index_funcs ());
+      objfile->qf.push_front
+	(per_bfd->cooked_index_table->make_quick_functions ());
       return;
     }
 
@@ -18682,6 +18683,12 @@ make_cooked_index_funcs ()
   return quick_symbol_functions_up (new cooked_index_functions);
 }
 
+quick_symbol_functions_up
+cooked_index_vector::make_quick_functions () const
+{
+  return make_cooked_index_funcs ();
+}
+
 
 
 /* Read the .debug_loclists or .debug_rnglists header (they are the same format)