fix #27135 and fix #27449 strong mode does not use propagated types

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 4ebd9b377a48a1fb58c0eb8d9fbc363f33f7cc6a..47e5599b9d5bee04b68a4c147da5c8e16745ffd6 100644
--- a/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
+++ b/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
@@ -2283,7 +2283,7 @@ class StaticTypeAnalyzer extends SimpleAstVisitor<Object> {
    * @param type the propagated type of the node
    */
   void _recordPropagatedType(Expression expression, DartType type) {
-    if (type != null && !type.isDynamic && !type.isBottom) {
+    if (!_strongMode && type != null && !type.isDynamic && !type.isBottom) {
       expression.propagatedType = type;
     }
   }
@@ -2299,6 +2299,9 @@ class StaticTypeAnalyzer extends SimpleAstVisitor<Object> {
    */
   void _recordPropagatedTypeOfFunction(
       ExecutableElement functionElement, FunctionBody body) {
+    if (_strongMode) {
+      return;
+    }
     DartType propagatedReturnType =
         _computePropagatedReturnTypeOfFunction(body);
     if (propagatedReturnType == null) {