Introduce wrapped_file

Simon pointed out that timestamped_file probably needed to implement a
few more methods.  This patch introduces a new file-wrapping file that
forwards most of its calls, making it simpler to implement new such
files.  It also converts timestamped_file and pager_file to use it.

Regression tested on x86-64 Fedora 34.

gdb/pager.h

@@ -23,16 +23,21 @@
 
 /* A ui_file that implements output paging and unfiltered output.  */
 
-class pager_file : public ui_file
+class pager_file : public wrapped_file
 {
 public:
   /* Create a new pager_file.  The new object takes ownership of
      STREAM.  */
   explicit pager_file (ui_file *stream)
-    : m_stream (stream)
+    : wrapped_file (stream)
   {
   }
 
+  ~pager_file ()
+  {
+    delete m_stream;
+  }
+
   DISABLE_COPY_AND_ASSIGN (pager_file);
 
   void write (const char *buf, long length_buf) override;
@@ -44,31 +49,11 @@ public:
     m_stream->write_async_safe (buf, length_buf);
   }
 
-  bool term_out () override
-  {
-    return m_stream->term_out ();
-  }
-
-  bool isatty () override
-  {
-    return m_stream->isatty ();
-  }
-
-  bool can_emit_style_escape () override
-  {
-    return m_stream->can_emit_style_escape ();
-  }
-
   void emit_style_escape (const ui_file_style &style) override;
   void reset_style () override;
 
   void flush () override;
 
-  int fd () const override
-  {
-    return m_stream->fd ();
-  }
-
   void wrap_here (int indent) override;
 
   void puts_unfiltered (const char *str) override
@@ -98,9 +83,6 @@ private:
   /* The style applied at the time that wrap_here was called.  */
   ui_file_style m_wrap_style;
 
-  /* The unfiltered output stream.  */
-  ui_file_up m_stream;
-
   /* This is temporarily set when paging.  This will cause some
      methods to change their behavior to ignore the wrap buffer.  */
   bool m_paging = false;

gdb/ui-file.h

@@ -391,32 +391,74 @@ public:
   }
 };
 
-/* A ui_file that optionally puts a timestamp at the start of each
-   line of output.  */
+/* A base class for ui_file types that wrap another ui_file.  */
 
-class timestamped_file : public ui_file
+class wrapped_file : public ui_file
 {
 public:
-  explicit timestamped_file (ui_file *stream)
-    : m_stream (stream)
-  {
-  }
+
+  bool isatty () override
+  { return m_stream->isatty (); }
+
+  bool term_out () override
+  { return m_stream->term_out (); }
 
   bool can_emit_style_escape () override
   { return m_stream->can_emit_style_escape (); }
 
+  void flush () override
+  { m_stream->flush (); }
+
+  void wrap_here (int indent) override
+  { m_stream->wrap_here (indent); }
+
+  void emit_style_escape (const ui_file_style &style) override
+  { m_stream->emit_style_escape (style); }
+
+  /* Rest the current output style to the empty style.  */
+  void reset_style () override
+  { m_stream->reset_style (); }
+
+  int fd () const override
+  { return m_stream->fd (); }
+
+  void puts_unfiltered (const char *str) override
+  { m_stream->puts_unfiltered (str); }
+
   void write_async_safe (const char *buf, long length_buf) override
   { return m_stream->write_async_safe (buf, length_buf); }
 
+protected:
+
+  /* Note that this class does not assume ownership of the stream.
+     However, a subclass may choose to, by adding a 'delete' to its
+     destructor.  */
+  explicit wrapped_file (ui_file *stream)
+    : m_stream (stream)
+  {
+  }
+
+  /* The underlying stream.  */
+  ui_file *m_stream;
+};
+
+/* A ui_file that optionally puts a timestamp at the start of each
+   line of output.  */
+
+class timestamped_file : public wrapped_file
+{
+public:
+  explicit timestamped_file (ui_file *stream)
+    : wrapped_file (stream)
+  {
+  }
+
   DISABLE_COPY_AND_ASSIGN (timestamped_file);
 
   void write (const char *buf, long len) override;
 
 private:
 
-  /* Output is sent here.  */
-  ui_file *m_stream;
-
   /* True if the next output should be timestamped.  */
   bool m_needs_timestamp = true;
 };