Infer Null for return type of functions with empty returns.

pkg/analyzer/lib/src/task/strong/checker.dart

Index: pkg/analyzer/lib/src/task/strong/checker.dart
diff --git a/pkg/analyzer/lib/src/task/strong/checker.dart b/pkg/analyzer/lib/src/task/strong/checker.dart
index 62bb922a87177129234ce3a1ad42ede429bb5bb6..491b50a6703913089c0f861a7cca12038e01a1b4 100644
--- a/pkg/analyzer/lib/src/task/strong/checker.dart
+++ b/pkg/analyzer/lib/src/task/strong/checker.dart
@@ -53,9 +53,10 @@ DartType _elementType(Element e) {
 
 Element _getKnownElement(Expression expression) {
   if (expression is ParenthesizedExpression) {
-    expression = (expression as ParenthesizedExpression).expression;
-  }
-  if (expression is FunctionExpression) {
+    return _getKnownElement(expression.expression);
+  } else if (expression is NamedExpression) {

[Leaf, 2017/02/06 18:27:15]

This fixes 28630, where we were not treating named parameters as concrete
functions.

[Jennifer Messerly, 2017/02/06 20:08:09]

wow this bug has been here for like ever. nice fix!

+    return _getKnownElement(expression.expression);
+  } else if (expression is FunctionExpression) {
     return expression.element;
   } else if (expression is PropertyAccess) {
     return expression.propertyName.staticElement;