Clean up LayoutInstabilityAPI REF.

Bug: 581518
Change-Id: Ibd6a02dadcc9d90d26d20fb827d2c5bdfb52b3d5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1831948Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Commit-Queue: Steve Kobes <skobes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701846}

third_party/blink/renderer/core/layout/layout_shift_tracker.cc

@@ -303,9 +303,7 @@ void LayoutShiftTracker::ReportShift(double score_delta,
     }
   }
 
-  if (RuntimeEnabledFeatures::LayoutInstabilityAPIEnabled(
-          frame.GetDocument()) &&
-      frame.DomWindow()) {
+  if (frame.DomWindow()) {
     WindowPerformance* performance =
         DOMWindowPerformance::performance(*frame.DomWindow());
     if (performance) {

third_party/blink/renderer/core/timing/layout_shift.idl

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 // https://wicg.github.io/layout-instability/#sec-layout-shift
-[Exposed=Window, RuntimeEnabled=LayoutInstabilityAPI]
+[Exposed=Window]
 interface LayoutShift : PerformanceEntry {
     readonly attribute double value;
     readonly attribute boolean hadRecentInput;

third_party/blink/renderer/core/timing/performance_observer.cc

@@ -66,8 +66,7 @@ Vector<AtomicString> PerformanceObserver::supportedEntryTypes(
       supportedEntryTypes.push_back(
           performance_entry_names::kLargestContentfulPaint);
     }
-    if (RuntimeEnabledFeatures::LayoutInstabilityAPIEnabled(execution_context))
-      supportedEntryTypes.push_back(performance_entry_names::kLayoutShift);
+    supportedEntryTypes.push_back(performance_entry_names::kLayoutShift);
     supportedEntryTypes.push_back(performance_entry_names::kLongtask);
   }
   supportedEntryTypes.push_back(performance_entry_names::kMark);

third_party/blink/renderer/core/timing/window_performance.cc

@@ -425,8 +425,6 @@ void WindowPerformance::DispatchFirstInputTiming(
 void WindowPerformance::AddLayoutShiftValue(double value,
                                             bool input_detected,
                                             base::TimeTicks input_timestamp) {
-  DCHECK(RuntimeEnabledFeatures::LayoutInstabilityAPIEnabled(
-      GetExecutionContext()));
   auto* entry = MakeGarbageCollected<LayoutShift>(
       now(), value, input_detected,
       input_detected ? MonotonicTimeToDOMHighResTimeStamp(input_timestamp)

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -856,13 +856,6 @@
       name: "LargestContentfulPaint",
       status: "stable",
     },
-    {
-      // Exposes layout shift scores to Javascript. See explainer:
-      // http://bit.ly/lsm-explainer.
-      name: "LayoutInstabilityAPI",
-      origin_trial_feature_name: "LayoutJankAPI",
-      status: "stable",
-    },
     {
       name: "LayoutNG",
       implied_by: ["LayoutNGBlockFragmentation", "LayoutNGFieldset", "LayoutNGFlexBox", "LayoutNGFragmentItem", "LayoutNGLineCache", "EditingNG", "BidiCaretAffinity", "LayoutNGTable"],