[scheduler] Actually enable high-priority input by default.

This change was dropped from
https://chromium-review.googlesource.com/c/chromium/src/+/1102505 due to
a bad merge. Add it back.

R=eseckler@chromium.org
BUG=806271

Change-Id: I6dc5f83cfe61ccbad3069e7d194c1dc494909ff9
Reviewed-on: https://chromium-review.googlesource.com/1145437Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577147}

third_party/blink/renderer/platform/scheduler/child/features.h

@@ -11,7 +11,7 @@ namespace blink {
 namespace scheduler {
 
 const base::Feature kHighPriorityInputOnMainThread{
-    "BlinkSchedulerHighPriorityInput", base::FEATURE_DISABLED_BY_DEFAULT};
+    "BlinkSchedulerHighPriorityInput", base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kHighPriorityInputOnCompositorThread{
     "BlinkSchedulerHighPriorityInputOnCompositorThread",