[heap] Use TimeTicks::Now() also for incremental_marking_start_time_

NotifyIncrementalMarkingStart() was using a different timer in the
default configuration to set incremental_marking_start_time_.

Bug: v8:11801
Change-Id: I1551bcc659d025bf8c46c865f5d2bd429934f628
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2930158Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74878}

src/heap/gc-tracer.cc

@@ -1155,7 +1155,7 @@ bool GCTracer::SurvivalEventsRecorded() const {
 void GCTracer::ResetSurvivalEvents() { recorded_survival_ratios_.Reset(); }
 
 void GCTracer::NotifyIncrementalMarkingStart() {
-  incremental_marking_start_time_ = heap_->MonotonicallyIncreasingTimeInMs();
+  incremental_marking_start_time_ = MonotonicallyIncreasingTimeInMs();
 }
 
 void GCTracer::FetchBackgroundMarkCompactCounters() {