Fix incorrect vector clear on mismatch

This bug seem a typo while migrating to support two thread (IO + UI).
I suspect they forgot to rewrite that use case.

Bug: 1093719
Change-Id: I7b8f8aecd6a7b126eee5af4035af69c5efdfd1cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2250509Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779494}

content/browser/scheduler/responsiveness/watcher.cc

@@ -100,7 +100,7 @@ void Watcher::DidRunTask(const base::PendingTask* task,
     *mismatched_task_identifiers += 1;
     // Mismatches can happen, so just ignore them for now. See
     // https://crbug.com/929813 and https://crbug.com/931874 for details.
-    return currently_running_metadata_ui_.clear();
+    return currently_running_metadata->clear();
   }
 
   const Metadata metadata = currently_running_metadata->back();