Add DCHECK in InsertPerformanceEntry

There is a reported crash in cases where InsertPerformanceEntry is
called, so add a DCHECK to make debugging easier and determine whether
this is indeed the problem or if it's something else. Also cleanup the
method.

Bug: 1141666
Change-Id: I9d15ff62255b4830ce7abf9fd7569b15195b6524
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495343Reviewed-by: Steve Kobes <skobes@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821396}

third_party/blink/renderer/core/timing/performance_user_timing.cc

@@ -35,23 +35,24 @@
 
 namespace blink {
 
-UserTiming::UserTiming(Performance& performance) : performance_(&performance) {}
+namespace {
 
-static void InsertPerformanceEntry(PerformanceEntryMap& performance_entry_map,
-                                   PerformanceEntry& entry) {
+void InsertPerformanceEntry(PerformanceEntryMap& performance_entry_map,
+                            PerformanceEntry& entry) {
   PerformanceEntryMap::iterator it = performance_entry_map.find(entry.name());
   if (it != performance_entry_map.end()) {
-    it->value->push_back(&entry);
+    DCHECK(it->value);
+    it->value->push_back(entry);
   } else {
     PerformanceEntryVector* vector =
-        MakeGarbageCollected<PerformanceEntryVector>(1);
-    (*vector)[0] = Member<PerformanceEntry>(entry);
+        MakeGarbageCollected<PerformanceEntryVector>();
+    vector->push_back(entry);
     performance_entry_map.Set(entry.name(), vector);
   }
 }
 
-static void ClearPeformanceEntries(PerformanceEntryMap& performance_entry_map,
-                                   const AtomicString& name) {
+void ClearPeformanceEntries(PerformanceEntryMap& performance_entry_map,
+                            const AtomicString& name) {
   if (name.IsNull()) {
     performance_entry_map.clear();
     return;
@@ -61,6 +62,10 @@ static void ClearPeformanceEntries(PerformanceEntryMap& performance_entry_map,
     performance_entry_map.erase(name);
 }
 
+}  // namespace
+
+UserTiming::UserTiming(Performance& performance) : performance_(&performance) {}
+
 void UserTiming::AddMarkToPerformanceTimeline(PerformanceMark& mark) {
   if (performance_->timing()) {
     TRACE_EVENT_COPY_MARK1("blink.user_timing", mark.name().Utf8().c_str(),