Clean up obsolete comments

This CL cleans up some TODO comments that have been completed.
Specifically, since crrev.com/c/2007791, we're using the
default-dictionary syntax.

Bug: 996275
TBR: npm@chromium.org
Change-Id: I55a77e1188fd78fadb9b83453a6bb65cef164449
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2059768Reviewed-by: Tom McKee <tommckee@chromium.org>
Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Commit-Queue: Tom McKee <tommckee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756665}

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

@@ -58,12 +58,8 @@ interface Performance : EventTarget {
 
     // User Timing
     // https://w3c.github.io/user-timing/#extensions-performance-interface
-    // TODO(https://crbug.com/996275): Once our IDL parser supports it, we need
-    // to supply a default-value of '{}' to markOptions.
     [MeasureAs=UserTiming, CallWith=ScriptState, RaisesException] PerformanceMark mark(DOMString markName, optional PerformanceMarkOptions markOptions = {});
     [MeasureAs=UserTiming] void clearMarks(optional DOMString markName);
-    // TODO(https://crbug.com/996275): Once our IDL parser supports it, we need
-    // to supply a default-value of '{}' to startOrOptions.
     [MeasureAs=UserTiming, CallWith=ScriptState, RaisesException] PerformanceMeasure measure(DOMString measureName, optional (DOMString or PerformanceMeasureOptions) startOrMeasureOptions = {}, optional DOMString endMark);
     [MeasureAs=UserTiming] void clearMeasures(optional DOMString measureName);