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

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

Index: pkg/analyzer/lib/src/generated/static_type_analyzer.dart
diff --git a/pkg/analyzer/lib/src/generated/static_type_analyzer.dart b/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
index 10e6f6b38d342767d4c3be7efef77c0f0fc7ab49..ebbf5edea4d5178d6a1abf9824088760f1b17ee1 100644
--- a/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
+++ b/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
@@ -1282,10 +1282,12 @@ class StaticTypeAnalyzer extends SimpleAstVisitor<Object> {
     if (initializer != null) {
       DartType rightType = initializer.bestType;
       SimpleIdentifier name = node.name;
-      _recordPropagatedType(name, rightType);
       VariableElement element = name.staticElement as VariableElement;
       if (element != null) {
         _resolver.overrideVariable(element, rightType, true);
+        if (_isReallyMoreSpecificThan(rightType, element.type)) {

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

Shouldn't this test be moved into _recordPropagatedType?

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

Maybe.
It takes Expression, so we would need to add the "staticType" parameter.
I will review all the other places in the following CL.

+          _recordPropagatedType(name, rightType);
+        }
       }
     }
     return null;
@@ -1880,6 +1882,22 @@ class StaticTypeAnalyzer extends SimpleAstVisitor<Object> {
     map["video"] = "VideoElement";
     return map;
   }
+
+  /**
+   * Return `true` if [propagatedType] is more specific than [staticType].
+   * In addition to [DartType.isMoreSpecificThan], we need to check that
+   * [propagatedType] is not the same as [staticType].
+   */
+  static bool _isReallyMoreSpecificThan(
+      DartType propagatedType, DartType staticType) {
+    if (propagatedType == null) {
+      return false;
+    }
+    if (propagatedType == staticType) {
+      return false;
+    }
+    return propagatedType.isMoreSpecificThan(staticType);
+  }
 }
 
 class _StaticTypeAnalyzer_computePropagatedReturnTypeOfFunction