Add FunctionType.getNamedParameter.

pkg/kernel/lib/ast.dart

Index: pkg/kernel/lib/ast.dart
diff --git a/pkg/kernel/lib/ast.dart b/pkg/kernel/lib/ast.dart
index f051b14ade22132f252350ab363b45c0099bf252..e39b541f09aa669e711d88d72b5bb6bd4a617dff 100644
--- a/pkg/kernel/lib/ast.dart
+++ b/pkg/kernel/lib/ast.dart
@@ -3991,6 +3991,26 @@ class FunctionType extends DartType {
         namedParameters: namedParameters);
   }
 
+  /// Looks up the type of the named parameter with the given name.
+  ///
+  /// Returns `null` if there is no named parameter with the given name.
+  DartType getNamedParameter(String name) {
+    int lower = 0;
+    int upper = namedParameters.length - 1;
+    while (lower <= upper) {
+      int pivot = (lower + upper) ~/ 2;
+      int comparison = name.compareTo(namedParameters[pivot].name);

[scheglov, 2017/05/10 18:03:35]

It should be slightly faster to extract `namedParameters[pivot]` into a local
variable and reuse when we found the name.

[Paul Berry, 2017/05/10 18:16:08]

Done.

+      if (comparison == 0) {
+        return namedParameters[pivot].type;
+      } else if (comparison < 0) {
+        upper = pivot - 1;
+      } else {
+        lower = pivot + 1;
+      }
+    }
+    return null;
+  }
+
   int get hashCode => _hashCode ??= _computeHashCode();
 
   int _computeHashCode() {