Resolve variable declaration in 'when' subject

compiler/psi/src/org/jetbrains/kotlin/psi/KtWhenExpression.java

@@ -35,6 +35,11 @@ public class KtWhenExpression extends KtExpressionImpl {
         return findChildrenByType(KtNodeTypes.WHEN_ENTRY);
     }
 
+    @Nullable
+    public KtProperty getSubjectVariable() {
+        return findChildByClass(KtProperty.class);
+    }
+
     @Nullable
     public KtExpression getSubjectExpression() {
         return findChildByClass(KtExpression.class);