Fix devtools timeline test

This test calls generateJSFrame after createPerformanceModelWithEvents,
except this already calls generateJSFrames. It just happens that this
is idempotent under some circumstances which this test narrowly falls
into. This meant that `events` was always empty and thus the merge
did not. Remove all this. Test results are still the same.

Bug: 1127827
Change-Id: I6c1d0d776bf692f3563583ea4fa72d1fff9ea3b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2455706Reviewed-by: Paul Lewis <aerotwist@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814636}

third_party/blink/web_tests/http/tests/devtools/tracing/timeline-js/timeline-js-callstacks.js

@@ -498,11 +498,8 @@
     }
   ];
 
-  var model = PerformanceTestRunner.createPerformanceModelWithEvents(rawTraceEvents);
-  var events = TimelineModel.TimelineJSProfileProcessor.generateJSFrameEvents(PerformanceTestRunner.mainTrackEvents());
-  events =
-      events.mergeOrdered(PerformanceTestRunner.mainTrackEvents(), SDK.TracingModel.Event.orderedCompareStartTime);
-  events
+  PerformanceTestRunner.createPerformanceModelWithEvents(rawTraceEvents);
+  PerformanceTestRunner.mainTrackEvents()
       .filter(function(e) {
         return e.duration;
       })