Fix type inference of getters that "override" setters and vice versa.

pkg/front_end/lib/src/fasta/kernel/kernel_class_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_class_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_class_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_class_builder.dart
index 7630c71e5cf8096a63744be0fe88cd75a57bd228..cde2c48bfae47204ad694cbec904c1c40a0526c5 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_class_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_class_builder.dart
@@ -182,6 +182,7 @@ abstract class KernelClassBuilder
 
   void checkOverrides(ClassHierarchy hierarchy) {
     hierarchy.forEachOverridePair(cls, checkOverride);
+    hierarchy.forEachCrossOverridePair(cls, handleCrossOverride);
   }
 
   void checkOverride(
@@ -208,6 +209,17 @@ abstract class KernelClassBuilder
     }
   }
 
+  void handleCrossOverride(
+      Member declaredMember, Member interfaceMember, bool isSetter) {
+    // Record any cases where a field or getter/setter has a corresponding (but
+    // opposite) getter/setter in a superclass, since this information will be
+    // needed for type inference.
+    if (declaredMember is KernelMember &&
+        identical(declaredMember.enclosingClass, cls)) {
+      KernelMember.recordCrossOverride(declaredMember, interfaceMember);
+    }
+  }
+
   void checkMethodOverride(
       Procedure declaredMember, Procedure interfaceMember) {
     if (declaredMember.enclosingClass != cls) {