Emit notes from ReportClassRequiresTraceMethod in deterministic order

Previously, the notes would be emitted in the iteration order over Fields,
which is an std::map<clang::FieldDecl*, FieldPoint>, which is ordered
by pointer value of FieldDecls. This would cause tests to flakily fail
on the Windows buildbots.

I'm not sure what caused these errors to start appearing right now,
but this should fix it.

BUG=581782

Review URL: https://codereview.chromium.org/1645613003

Cr-Commit-Position: refs/heads/master@{#372016}

tools/clang/blink_gc_plugin/BlinkGCPluginConsumer.cpp

@@ -973,19 +973,23 @@ void BlinkGCPluginConsumer::ReportClassRequiresTraceMethod(RecordInfo* info) {
                    diag_class_requires_trace_method_)
       << info->record();
 
-  for (RecordInfo::Bases::iterator it = info->GetBases().begin();
-       it != info->GetBases().end();
-       ++it) {
-    if (it->second.NeedsTracing().IsNeeded())
-      NoteBaseRequiresTracing(&it->second);
+  // Use an intermediate map to sort the notes by source location.
+  std::map<clang::SourceLocation, BasePoint*> BaseNotes;
+  for (auto& pair : info->GetBases()) {
+    if (pair.second.NeedsTracing().IsNeeded())
+      BaseNotes.insert(std::make_pair(pair.first->getLocStart(), &pair.second));
   }
-
-  for (RecordInfo::Fields::iterator it = info->GetFields().begin();
-       it != info->GetFields().end();
-       ++it) {
-    if (!it->second.IsProperlyTraced())
-      NoteFieldRequiresTracing(info, it->first);
+  for (auto& pair : BaseNotes)
+    NoteBaseRequiresTracing(pair.second);
+
+  // Use an intermediate map to sort the notes by source location.
+  std::map<clang::SourceLocation, clang::FieldDecl*> FieldNotes;
+  for (auto& pair : info->GetFields()) {
+    if (!pair.second.IsProperlyTraced())
+      FieldNotes.insert(std::make_pair(pair.first->getLocStart(), pair.first));
   }
+  for (auto& pair : FieldNotes)
+    NoteFieldRequiresTracing(info, pair.second);
 }
 
 void BlinkGCPluginConsumer::ReportBaseRequiresTracing(