[macOS Capture] Make AVFoundationCaptureV2 convert to NV12 by default.

This CL makes "InCaptureConvertToNv12" enabled-by-default. Because this
path is only used by the "AVFoundationCaptureV2" path, the result of
this is that our "AVFoundationCaptureV2" experiment will transform all
frames to NV12 in M88.

Performance impact indicated below when running:
https://webrtc.github.io/samples/src/content/getusermedia/resolution/
This is comparing AVFoundationCaptureV2 with or without
InCaptureConvertToNv12.

Logitech C920 Full HD (MJPEG):
  Old path MJPEG -> I420 SW buffer: 8.71 W
  New path MJPEG -> NV12 IOSurface: 7.88 W (-0.83 W)

Logitech C920 VGA (YUVS):
  Old path YUVS -> I420 SW buffer: 6.62 W
  New path YUVS -> NV12 IOSurface: 6.49 W (-0.13 W)

Facetime HD (NV12):
  Triggers pass-through path, same as before.

Bug: chromium:1132299
Change-Id: Iede80be8407373a39c87a9b042168fbb43a15809
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532558
Commit-Queue: Henrik Boström <hbos@chromium.org>
Reviewed-by: Evan Shrubsole <eshr@google.com>
Reviewed-by: Ilya Nikolaevskiy <ilnik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826736}

media/capture/video/mac/sample_buffer_transformer_mac.cc

@@ -16,7 +16,7 @@
 namespace media {
 
 const base::Feature kInCaptureConvertToNv12{"InCaptureConvertToNv12",
-                                            base::FEATURE_DISABLED_BY_DEFAULT};
+                                            base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kInCaptureConvertToNv12WithPixelTransfer{
     "InCaptureConvertToNv12WithPixelTransfer",

media/capture/video/mac/sample_buffer_transformer_mac_unittest.mm

@@ -408,8 +408,8 @@ INSTANTIATE_TEST_SUITE_P(SampleBufferTransformerTest,
                          TestParametersOSTypeToString);
 
 TEST(SampleBufferTransformerAutoReconfigureTest,
-     AutoReconfigureDisabledByDefault) {
-  EXPECT_FALSE(SampleBufferTransformer::CreateIfAutoReconfigureEnabled());
+     AutoReconfigureIsEnabledByDefault) {
+  EXPECT_TRUE(SampleBufferTransformer::CreateIfAutoReconfigureEnabled());
 }
 
 TEST(SampleBufferTransformerAutoReconfigureTest,