media: enable ChromeosVideoDecoder feature

We already enable ChromeosVideoDecoder feature at stable channel for 2
weeks. It's time to enable it by default.

Bug: 984482
Test: ninja media/base
Change-Id: I905d12fb0a53f16b76afd4975f90db6013e07b9a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2035212Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Chih-Yu Huang <akahuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738037}

media/base/media_switches.cc

@@ -280,7 +280,7 @@ const base::Feature kRevokeMediaSourceObjectURLOnAttach{
 // Enable the instance from ChromeosVideoDecoderFactory in
 // MojoVideoDecoderService, replacing VdaVideoDecoder at Chrome OS platform.
 const base::Feature kChromeosVideoDecoder{"ChromeosVideoDecoder",
-                                          base::FEATURE_DISABLED_BY_DEFAULT};
+                                          base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enable saving playback information in a crash trace, to see if some codecs
 // are crashier than others.