Harmlessly qualify classes as final (or explicitly comment not)...

... Should have no effect on generated code, except perhaps some slight faster
virtual function calls.  Mostly useful as documentation of design intent.

Tried to mark every one of our classes that inherits from another, or is a
base for others, or has abstract virtual functions, and a few others besides.

src/ondemand/ODComputeSummaryTask.h

@@ -26,7 +26,7 @@ class ODPCMAliasBlockFile;
 class WaveTrack;
 
 /// A class representing a modular task to be used with the On-Demand structures.
-class ODComputeSummaryTask:public ODTask
+class ODComputeSummaryTask final : public ODTask
 {
  public:
 

src/ondemand/ODDecodeFFmpegTask.cpp

@@ -52,7 +52,7 @@ typedef struct _FFmpegDecodeCache
 //------ ODFFmpegDecoder declaration and defs - here because we strip dependencies from .h files
 
 ///class to decode a particular file (one per file).  Saves info such as filename and length (after the header is read.)
-class ODFFmpegDecoder:public ODFileDecoder
+class ODFFmpegDecoder final : public ODFileDecoder
 {
 
 

src/ondemand/ODDecodeFFmpegTask.h

@@ -23,7 +23,7 @@
 class ODFileDecoder;
 class WaveTrack;
 /// A class representing a modular task to be used with the On-Demand structures.
-class ODDecodeFFmpegTask:public ODDecodeTask
+class ODDecodeFFmpegTask final : public ODDecodeTask
 {
  public:
 

src/ondemand/ODDecodeFlacTask.h

@@ -42,7 +42,7 @@ class ODFlacDecoder;
 class ODFLACFile;
 
 /// A class representing a modular task to be used with the On-Demand structures.
-class ODDecodeFlacTask:public ODDecodeTask
+class ODDecodeFlacTask final : public ODDecodeTask
 {
  public:
 
@@ -61,7 +61,7 @@ class ODDecodeFlacTask:public ODDecodeTask
 };
 
 
-class ODFLACFile : public FLAC::Decoder::File
+class ODFLACFile final : public FLAC::Decoder::File
 {
  public:
    ODFLACFile(ODFlacDecoder *decoder) : mDecoder(decoder)
@@ -91,7 +91,7 @@ class ODFLACFile : public FLAC::Decoder::File
 
 
 ///class to decode a particular file (one per file).  Saves info such as filename and length (after the header is read.)
-class ODFlacDecoder:public ODFileDecoder
+class ODFlacDecoder final : public ODFileDecoder
 {
    friend class ODFLACFile;
 public:

src/ondemand/ODDecodeTask.h

@@ -37,7 +37,7 @@ class ODFileDecoder;
 
 
 /// A class representing a modular task to be used with the On-Demand structures.
-class ODDecodeTask:public ODTask
+class ODDecodeTask /* not final */ : public ODTask
 {
  public:
    ODDecodeTask();
@@ -96,7 +96,7 @@ protected:
 };
 
 ///class to decode a particular file (one per file).  Saves info such as filename and length (after the header is read.)
-class ODFileDecoder
+class ODFileDecoder /* not final */
 {
 public:
    ///This should handle unicode converted to UTF-8 on mac/linux, but OD TODO:check on windows

src/ondemand/ODManager.h

@@ -40,7 +40,7 @@ int CompareNoCaseFileName(const wxString& first, const wxString& second);
 /// number of threads.
 class WaveTrack;
 class ODWaveTrackTaskQueue;
-class ODManager
+class ODManager final
 {
  public:
    ///Gets the singleton instance - this is a function pointer that points to one of the below two instance calls.
@@ -212,7 +212,7 @@ class ODManagerHelperThread {
    int mPriority;
 };
 #else
-   class ODManagerHelperThread : public wxThread
+   class ODManagerHelperThread final : public wxThread
    {
       public:
       ///Constructs a ODTaskThread

src/ondemand/ODTask.h

@@ -35,7 +35,7 @@ class WaveTrack;
 DECLARE_EXPORTED_EVENT_TYPE(AUDACITY_DLL_API, EVT_ODTASK_COMPLETE, -1)
 
 /// A class representing a modular task to be used with the On-Demand structures.
-class ODTask
+class ODTask /* not final */
 {
  public:
    enum {

src/ondemand/ODTaskThread.h

@@ -125,7 +125,7 @@ protected:
 #else
 
 
-class ODTaskThread : public wxThread
+class ODTaskThread final : public wxThread
 {
 public:
    ///Constructs a ODTaskThread
@@ -142,7 +142,7 @@ protected:
 
 
 //a wrapper for wxMutex.
-class AUDACITY_DLL_API ODLock : public wxMutex
+class AUDACITY_DLL_API ODLock final : public wxMutex
 {
 public:
    ///Constructs a ODTaskThread
@@ -151,7 +151,7 @@ public:
   virtual ~ODLock(){}
 };
 
-class ODCondition : public wxCondition
+class ODCondition final : public wxCondition
 {
 public:
    ODCondition(ODLock *lock):wxCondition(*lock){}

src/ondemand/ODWaveTrackTaskQueue.h

@@ -28,7 +28,7 @@ tasks associated with a WaveTrack.
 class WaveTrack;
 class ODTask;
 /// A class representing a modular task to be used with the On-Demand structures.
-class ODWaveTrackTaskQueue
+class ODWaveTrackTaskQueue final
 {
  public: