Always record inference of implicit function expression params, even if dynamic.

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

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
@@ skipping 409 matching lines @@
       // recovery path.
       substitution = Substitution.empty;
     }
 
     // Define `Ri` as follows: if `Pi` is not `_`, let `Ri` be `Pi`.
     // Otherwise, if `Qi` is not `_`, let `Ri` be the greatest closure of
     // `Qi[T/S]` with respect to `?`.  Otherwise, let `Ri` be `dynamic`.
     for (int i = 0; i < formals.length; i++) {
       KernelVariableDeclaration formal = formals[i];
       if (KernelVariableDeclaration.isImplicitlyTyped(formal)) {
+        DartType inferredType;
         if (formalTypesFromContext[i] != null) {
-          var inferredType = greatestClosure(inferrer.coreTypes,
+          inferredType = greatestClosure(inferrer.coreTypes,
               substitution.substituteType(formalTypesFromContext[i]));
-          inferrer.instrumentation?.record(
-              Uri.parse(inferrer.uri),
-              formal.fileOffset,
-              'type',
-              new InstrumentationValueForType(inferredType));
-          formal.type = inferredType;
+        } else {
+          inferredType = const DynamicType();
         }
+        inferrer.instrumentation?.record(
+            Uri.parse(inferrer.uri),
+            formal.fileOffset,
+            'type',
+            new InstrumentationValueForType(inferredType));
+        formal.type = inferredType;
       }
     }
 
     // Let `N'` be `N[T/S]`.  The [ClosureContext] constructor will adjust
     // accordingly if the closure is declared with `async`, `async*`, or
     // `sync*`.
     if (returnContext != null) {
       returnContext = substitution.substituteType(returnContext);
     }
 
@@ skipping 868 matching lines @@
           closureContext.isAsync
               ? inferrer.coreTypes.streamClass
               : inferrer.coreTypes.iterableClass);
     }
     var inferredType = inferrer.inferExpression(
         expression, typeContext, closureContext != null);
     closureContext?.handleYield(inferrer, isYieldStar, inferredType);
     inferrer.listener.yieldStatementExit(this);
   }
 }