Resolve DCHECK issues for fetching timer.

This looks to be the only place that the timer can be running and
ScheduleFetch can be called.


Bug: 1111815
Change-Id: Ic7e3bdacb610e48ac7934e2ec2712ef80c92edb3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2332298
Commit-Queue: Michael Crouse <mcrouse@chromium.org>
Reviewed-by: Sophie Chang <sophiechang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793748}

chrome/browser/optimization_guide/optimization_guide_hints_manager.cc

@@ -565,7 +565,8 @@ void OptimizationGuideHintsManager::MaybeScheduleTopHostsHintsFetch() {
   if (optimization_guide::switches::ShouldOverrideFetchHintsTimer()) {
     SetLastHintsFetchAttemptTime(clock_->Now());
     FetchTopHostsHints();
-  } else {
+  } else if (!top_hosts_hints_fetch_timer_.IsRunning()) {
+    // Only Schedule this is the time is not already running.
     ScheduleTopHostsHintsFetch();
   }
 }