Fix for missing interface targets when not in strong mode.

pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart

Index: pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
index 8d7f4bf6f872c93b4a909ea341c452e6d2cf432a..fcbf81920b6cfb44cd3d725718c7cda74d66c322 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
@@ -326,13 +326,17 @@ abstract class TypeInferrerImpl extends TypeInferrer {
       var interfaceMember = findInterfaceMember(
           receiverType, methodInvocation.name, methodInvocation.fileOffset,
           silent: silent);
-      methodInvocation.interfaceTarget = interfaceMember;
+      if (strongMode) {
+        methodInvocation.interfaceTarget = interfaceMember;
+      }
       return interfaceMember;
     } else if (methodInvocation is SuperMethodInvocation) {
       var interfaceMember = findInterfaceMember(
           receiverType, methodInvocation.name, methodInvocation.fileOffset,
           silent: silent);
-      methodInvocation.interfaceTarget = interfaceMember;
+      if (strongMode) {
+        methodInvocation.interfaceTarget = interfaceMember;
+      }
       return interfaceMember;
     } else {
       throw internalError(