Type tracing bug fix for issue 28919.

pkg/compiler/lib/src/inferrer/type_graph_dump.dart

Index: pkg/compiler/lib/src/inferrer/type_graph_dump.dart
diff --git a/pkg/compiler/lib/src/inferrer/type_graph_dump.dart b/pkg/compiler/lib/src/inferrer/type_graph_dump.dart
index 5f786caa1fd25a65ebb33098e6e7a3134a082790..13a7e7b19a8ed9fefab8b6c6b976e9873fd8528d 100644
--- a/pkg/compiler/lib/src/inferrer/type_graph_dump.dart
+++ b/pkg/compiler/lib/src/inferrer/type_graph_dump.dart
@@ -8,6 +8,7 @@ import '../elements/elements.dart';
 import '../types/types.dart';
 import 'inferrer_engine.dart';
 import 'type_graph_nodes.dart';
+import 'debug.dart';
 
 /// Dumps the type inference graph in Graphviz Dot format into the `typegraph`
 /// subfolder of the current working directory. Each function body is dumped in
@@ -79,7 +80,7 @@ class TypeGraphDump {
             .outputProvider('$outputDir/$name', 'dot', OutputType.debug);
         _GraphGenerator visitor = new _GraphGenerator(this, element, output);
         for (TypeInformation node in nodes[element]) {
-          node.accept(visitor);
+          visitor.visit(node);
         }
         visitor.addMissingNodes();
         visitor.finish();
@@ -169,11 +170,15 @@ class _GraphGenerator extends TypeInformationVisitor {
     while (worklist.isNotEmpty) {
       TypeInformation node = worklist.removeLast();
       assert(nodeId.containsKey(node));
-      if (seen.contains(node)) continue;
-      node.accept(this);
+      visit(node);
     }
   }
 
+  void visit(TypeInformation info) {
+    if (seen.contains(info)) return;
+    info.accept(this);
+  }
+
   void append(String string) {
     output..add(string)..add('\n');
   }
@@ -311,14 +316,25 @@ class _GraphGenerator extends TypeInformationVisitor {
         }
       }
     }
+    if (PRINT_GRAPH_ALL_NODES) {
+      for (TypeInformation user in node.users) {
+        if (!isExternal(user)) {
+          visit(user);
+        }
+      }
+    }
   }
 
   void visitNarrowTypeInformation(NarrowTypeInformation info) {
+    // Omit unused Narrows.
+    if (!PRINT_GRAPH_ALL_NODES && info.users.isEmpty) return;
     addNode(info, 'Narrow\n${formatType(info.typeAnnotation)}',
         color: narrowColor);
   }
 
   void visitPhiElementTypeInformation(PhiElementTypeInformation info) {
+    // Omit unused Phis.
+    if (!PRINT_GRAPH_ALL_NODES && info.users.isEmpty) return;
     addNode(info, 'Phi ${info.variable?.name ?? ''}', color: phiColor);
   }