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: I93605e43f3a2f454e3a43e4cb370ac4d52f5330a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2508855
Auto-Submit: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823779}

diff --git a/media/renderers/renderer_impl.h b/media/renderers/renderer_impl.h
index ae226a7d..c33d290 100644
--- a/media/renderers/renderer_impl.h
+++ b/media/renderers/renderer_impl.h

@@ -41,7 +41,7 @@
 class VideoRenderer;
 class WallClockTimeSource;
 
-class MEDIA_EXPORT RendererImpl : public Renderer {
+class MEDIA_EXPORT RendererImpl final : public Renderer {
  public:
   // Renders audio/video streams using |audio_renderer| and |video_renderer|
   // provided. All methods except for GetMediaTime() run on the |task_runner|.