Add some type inference for "yield" statements.

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

Index: pkg/front_end/lib/src/fasta/kernel/body_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index 48bd0e053685a86c4fbea8f3a7340298214509bd..ff6d4eb0013035c9182867770f0074c68f32a997 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -18,7 +18,8 @@ import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart'
         KernelArguments,
         KernelField,
         KernelFunctionDeclaration,
-        KernelReturnStatement;
+        KernelReturnStatement,
+        KernelYieldStatement;
 
 import 'package:front_end/src/fasta/kernel/utils.dart' show offsetForToken;
 
@@ -2318,7 +2319,7 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
   @override
   void endYieldStatement(Token yieldToken, Token starToken, Token endToken) {
     debugEvent("YieldStatement");
-    push(new YieldStatement(popForValue(), isYieldStar: starToken != null)
+    push(new KernelYieldStatement(popForValue(), isYieldStar: starToken != null)
       ..fileOffset = yieldToken.charOffset);
   }