Rename FrameLayoutJank trace event to LayoutShift.

Also rename keys in the TracedValue to avoid the word "jank".

Bug: 963474
Change-Id: I598a9f80cdd873474292785a081f40cc923f9772
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627936
Auto-Submit: Steve Kobes <skobes@chromium.org>
Commit-Queue: Bryan McQuade <bmcquade@chromium.org>
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662884}

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

@@ -291,7 +291,7 @@ void JankTracker::NotifyPrePaintFinished() {
 #endif
 
   TRACE_EVENT_INSTANT2(
-      "loading", "FrameLayoutJank", TRACE_EVENT_SCOPE_THREAD, "data",
+      "loading", "LayoutShift", TRACE_EVENT_SCOPE_THREAD, "data",
       PerFrameTraceData(jank_fraction, jank_fraction_with_move_distance,
                         granularity_scale),
       "frame", ToTraceValue(&frame));
@@ -363,8 +363,8 @@ std::unique_ptr<TracedValue> JankTracker::PerFrameTraceData(
     double jank_fraction_with_move_distance,
     double granularity_scale) const {
   auto value = std::make_unique<TracedValue>();
-  value->SetDouble("jank_fraction", jank_fraction);
-  value->SetDouble("jank_fraction_with_move_distance",
+  value->SetDouble("score", jank_fraction);
+  value->SetDouble("score_with_move_distance",
                    jank_fraction_with_move_distance);
   value->SetDouble("cumulative_score", score_);
   value->SetDouble("cumulative_score_with_move_distance",