fix #27036, pass definite function types to LUB

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 34530f004eb136f67a48e468486fb151205de897..5f089988e9c1567dae421fa306c288d335f4a163 100644
--- a/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
+++ b/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
@@ -17,6 +17,7 @@ import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
+import 'package:analyzer/src/task/strong/checker.dart' show getDefiniteType;
 
 /**
  * Instances of the class `StaticTypeAnalyzer` perform two type-related tasks. First, they
@@ -1423,8 +1424,8 @@ class StaticTypeAnalyzer extends SimpleAstVisitor<Object> {
    */
   void _analyzeLeastUpperBound(
       Expression node, Expression expr1, Expression expr2) {
-    DartType staticType1 = _getStaticType(expr1);
-    DartType staticType2 = _getStaticType(expr2);
+    DartType staticType1 = _getDefiniteType(expr1);
+    DartType staticType2 = _getDefiniteType(expr2);
     if (staticType1 == null) {
       // TODO(brianwilkerson) Determine whether this can still happen.
       staticType1 = _dynamicType;
@@ -1653,6 +1654,17 @@ class StaticTypeAnalyzer extends SimpleAstVisitor<Object> {
   }
 
   /**
+   * Gets the definite type of expression, which can be used in cases where
+   * the most precise type is desired, for example computing the least upper
+   * bound.
+   *
+   * See [getDefiniteType] for more information. Without strong mode, this is
+   * equivalent to [_getStaticType].
+   */
+  DartType _getDefiniteType(Expression expr) =>
+      getDefiniteType(expr, _typeSystem, _typeProvider);
+
+  /**
    * If the given element name can be mapped to the name of a class defined within the given
    * library, return the type specified by the argument.
    *