Enable IOSurfaceCapturer feature by default on TOT

The IOSurfaceCapturer for MacOSX has great experiment results on all
channels. So move on to next step to enable it by default on TOT before
enabling it 100% everywhere.

Bug: 840597
Change-Id: I99f0dd64c3ce280173f89cb73012bbd3077f54a2
Reviewed-on: https://chromium-review.googlesource.com/1181921Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Weiyong Yao <braveyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584632}

content/public/common/content_features.cc

@@ -687,7 +687,7 @@ const base::Feature kDeviceMonitorMac{"DeviceMonitorMac",
 
 // Enable IOSurface based screen capturer.
 const base::Feature kIOSurfaceCapturer{"IOSurfaceCapturer",
-                                       base::FEATURE_DISABLED_BY_DEFAULT};
+                                       base::FEATURE_ENABLED_BY_DEFAULT};
 
 // The V2 sandbox on MacOS removes the unsandboed warmup phase and sandboxes the
 // entire life of the process.