Emit notes from ReportClassRequiresTraceMethod in deterministic order

tools/clang/blink_gc_plugin/BlinkGCPluginConsumer.cpp

Index: tools/clang/blink_gc_plugin/BlinkGCPluginConsumer.cpp
diff --git a/tools/clang/blink_gc_plugin/BlinkGCPluginConsumer.cpp b/tools/clang/blink_gc_plugin/BlinkGCPluginConsumer.cpp
index c90510e93d76fc67c8c98b886e7981f8bf61c4c0..6c52c7712a722b70ea744acc68675f01bb5d0e4f 100644
--- a/tools/clang/blink_gc_plugin/BlinkGCPluginConsumer.cpp
+++ b/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(