Fix a type inference corner case: return expression where void expected.

pkg/analyzer/test/src/context/mock_sdk.dart

Index: pkg/analyzer/test/src/context/mock_sdk.dart
diff --git a/pkg/analyzer/test/src/context/mock_sdk.dart b/pkg/analyzer/test/src/context/mock_sdk.dart
index 967ffb57bec8f9a835d8754a8b81929ef20dcc0b..b0e0513be580dcfcf4613ea05332b1ad01d3f866 100644
--- a/pkg/analyzer/test/src/context/mock_sdk.dart
+++ b/pkg/analyzer/test/src/context/mock_sdk.dart
@@ -270,6 +270,8 @@ abstract class Iterable<E> {
   Iterable/*<T>*/ expand/*<T>*/(Iterable/*<T>*/ f(E element));
 
   Iterable<E> where(bool test(E element));
+  
+  void forEach(void f(E element));
 
   List<E> toList();
 }