Add FunctionType.getNamedParameter.

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 73c98cc0ed765e42978d4ff155b6b30106497f2d..34b001722e5581411af4b7797ad98d86c41c5d9a 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
@@ -625,21 +625,7 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   }
 
   DartType _getNamedParameterType(FunctionType functionType, String name) {
-    // TODO(paulberry): is there a kernel function that does this binary search?
-    int lower = 0;
-    int upper = functionType.namedParameters.length - 1;
-    while (lower <= upper) {
-      int pivot = (lower + upper) ~/ 2;
-      int comparison = name.compareTo(functionType.namedParameters[pivot].name);
-      if (comparison == 0) {
-        return functionType.namedParameters[pivot].type;
-      } else if (comparison < 0) {
-        upper = pivot - 1;
-      } else {
-        lower = pivot + 1;
-      }
-    }
-    return const DynamicType();
+    return functionType.getNamedParameter(name) ?? const DynamicType();
   }
 
   DartType _getPositionalParameterType(FunctionType functionType, int i) {