Revert "AVFoundationCaptureV2: disable by default."

This reverts commit f37a0083.

Reason for revert: crbug.com/1128470 is back under control, let's
re-enable AVFoundationCaptureV2 by default.

Original change's description:
> AVFoundationCaptureV2: disable by default.
>
> Reason: breaks post-commit testcase.
>
> Bug: 1128470
> Change-Id: I6a6745e9ba8150dcac2408af1b73186ac05a75d6
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2421308
> Reviewed-by: Henrik Boström <hbos@chromium.org>
> Reviewed-by: Guido Urdaneta <guidou@chromium.org>
> Reviewed-by: Jochen Eisinger <jochen@chromium.org>
> Commit-Queue: Markus Handell <handellm@google.com>
> Cr-Commit-Position: refs/heads/master@{#808818}

TBR=hbos@chromium.org,guidou@chromium.org,jochen@chromium.org,handellm@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1128470
Change-Id: I81ee2900d9f3c0911211ee7fd83e1a335de707a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2439070Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Reviewed-by: Markus Handell <handellm@google.com>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811994}

media/base/media_switches.cc

@@ -658,7 +658,7 @@ const base::Feature MEDIA_EXPORT kMediaFoundationVP8Decoding{
 // Controls whether the next version mac capturer, including power improvements,
 // zero copy operation, and other improvements, is active.
 const base::Feature MEDIA_EXPORT kAVFoundationCaptureV2{
-    "AVFoundationCaptureV2", base::FEATURE_DISABLED_BY_DEFAULT};
+    "AVFoundationCaptureV2", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Controls whether or not the V2 capturer exports IOSurfaces for zero-copy.
 // This feature only has any effect if kAVFoundationCaptureV2 is also enabled.