Don't set a propagate type if the variable has already the same static type.

pkg/analyzer/lib/src/generated/element.dart

Index: pkg/analyzer/lib/src/generated/element.dart
diff --git a/pkg/analyzer/lib/src/generated/element.dart b/pkg/analyzer/lib/src/generated/element.dart
index 8863d044ae82e70dd7769b4385eafd00a11473c5..a7d8bf36f574b1bf226a6c6dc74941076755f9f9 100644
--- a/pkg/analyzer/lib/src/generated/element.dart
+++ b/pkg/analyzer/lib/src/generated/element.dart
@@ -6338,8 +6338,12 @@ class InterfaceTypeImpl extends TypeImpl implements InterfaceType {
   List<TypeParameterElement> get typeParameters => element.typeParameters;
 
   @override
-  bool operator ==(Object object) =>
-      internalEquals(object, new HashSet<ElementPair>());
+  bool operator ==(Object object) {
+    if (identical(object, this)) {

[Brian Wilkerson, 2015/03/03 14:53:49]

I'm not sure why this logic needs to be duplicated (both here and in
internalEquals).

[scheglov, 2015/03/03 15:02:17]

Here we have a chance to check quickly without creating a HashSet instance, e.g.
"int == int".
In internalEquals we short circuit equals for type used in other types, e.g.
"int" in "List<int> == List<int>"

+      return true;
+    }
+    return internalEquals(object, new HashSet<ElementPair>());
+  }
 
   @override
   void appendTo(StringBuffer buffer, Set<DartType> visitedTypes) {
@@ -6432,6 +6436,9 @@ class InterfaceTypeImpl extends TypeImpl implements InterfaceType {
 
   @override
   bool internalEquals(Object object, Set<ElementPair> visitedElementPairs) {
+    if (identical(object, this)) {
+      return true;
+    }
     if (object is! InterfaceTypeImpl) {
       return false;
     }