Mark classes with final dtors as final

- -Wfinal-dtor-non-final-class warns on classes with final dtors but
  not final classes.
- Error messages are better when the class is marked final.
- Fix existing issues in code base and a follow up will remove warning
  exemption.

Bug: 999886
Test: no errors building
Change-Id: Ie813762ce32bbebf26bf1f661ffacba67636ef92
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2508200
Auto-Submit: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: John Rummell <jrummell@chromium.org>
Reviewed-by: John Rummell <jrummell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823455}

media/cdm/cdm_adapter.h

@@ -37,7 +37,7 @@ class AudioFramesImpl;
 class CdmAuxiliaryHelper;
 class CdmWrapper;
 
-class MEDIA_EXPORT CdmAdapter : public ContentDecryptionModule,
+class MEDIA_EXPORT CdmAdapter final : public ContentDecryptionModule,
                                       public CdmContext,
                                       public Decryptor,
                                       public cdm::Host_10,

media/cdm/cdm_context_ref_impl.h

@@ -17,7 +17,7 @@ namespace media {
 
 class ContentDecryptionModule;
 
-class MEDIA_EXPORT CdmContextRefImpl : public CdmContextRef {
+class MEDIA_EXPORT CdmContextRefImpl final : public CdmContextRef {
  public:
   explicit CdmContextRefImpl(scoped_refptr<ContentDecryptionModule> cdm);
   ~CdmContextRefImpl() final;

media/cdm/cdm_helpers.h

@@ -19,7 +19,7 @@ namespace media {
 
 class VideoFrame;
 
-class DecryptedBlockImpl : public cdm::DecryptedBlock {
+class DecryptedBlockImpl final : public cdm::DecryptedBlock {
  public:
   DecryptedBlockImpl();
   ~DecryptedBlockImpl() final;
@@ -102,7 +102,7 @@ class MEDIA_EXPORT VideoFrameImpl : public cdm::VideoFrame,
   DISALLOW_COPY_AND_ASSIGN(VideoFrameImpl);
 };
 
-class AudioFramesImpl : public cdm::AudioFrames {
+class AudioFramesImpl final : public cdm::AudioFrames {
  public:
   AudioFramesImpl();
   ~AudioFramesImpl() final;

media/cdm/default_cdm_factory.h

@@ -13,7 +13,7 @@ namespace media {
 
 struct CdmConfig;
 
-class MEDIA_EXPORT DefaultCdmFactory : public CdmFactory {
+class MEDIA_EXPORT DefaultCdmFactory final : public CdmFactory {
  public:
   DefaultCdmFactory();
   ~DefaultCdmFactory() final;

media/cdm/library_cdm/clear_key_cdm/cdm_video_decoder.cc

@@ -161,7 +161,7 @@ void SetupGlobalEnvironmentIfNeeded() {
 // |kNestableTasksAllowed| because we could be running the RunLoop in a task,
 // e.g. in component builds when we share the same task runner as the host. In
 // a static build, this is not necessary.
-class VideoDecoderAdapter : public CdmVideoDecoder {
+class VideoDecoderAdapter final : public CdmVideoDecoder {
  public:
   VideoDecoderAdapter(CdmHostProxy* cdm_host_proxy,
                       std::unique_ptr<VideoDecoder> video_decoder)