Bug 1811750 - Eliminate redundant array filling in performance.measur…

…e r=sefeng

Basically we were falling off a cliff where if we had a bunch of marks recorded
with a particular name, when trying to measure we would fill an array with all
of them only to return the last one. This just replaces that by iterating in
reverse and returning the first matching mark. Arguably we should be using a
hashmap or something here, but this is a quick and trivial improvement that I
think will resolve the reported issue.

Differential Revision: https://phabricator.services.mozilla.com/D199451

dom/performance/Performance.cpp

@@ -396,17 +396,15 @@ DOMHighResTimeStamp Performance::ConvertMarkToTimestampWithString(
     return ConvertNameToTimestamp(aName, aRv);
   }
 
-  AutoTArray<RefPtr<PerformanceEntry>, 1> arr;
-  Optional<nsAString> typeParam;
-  nsAutoString str;
-  str.AssignLiteral("mark");
-  typeParam = &str;
-  GetEntriesByName(aName, typeParam, arr);
-  if (!arr.IsEmpty()) {
-    if (aReturnUnclamped) {
-      return arr.LastElement()->UnclampedStartTime();
+  RefPtr<nsAtom> name = NS_Atomize(aName);
+  // Just loop over the user entries
+  for (const PerformanceEntry* entry : Reversed(mUserEntries)) {
+    if (entry->GetName() == name && entry->GetEntryType() == nsGkAtoms::mark) {
+      if (aReturnUnclamped) {
+        return entry->UnclampedStartTime();
+      }
+      return entry->StartTime();
     }
-    return arr.LastElement()->StartTime();
   }
 
   nsPrintfCString errorMsg("Given mark name, %s, is unknown",