Fix implementation of fold() in analyzer's mock SDK.

pkg/front_end/testcases/inference/generic_methods_downwards_inference_fold.dart

Index: pkg/front_end/testcases/inference/generic_methods_downwards_inference_fold.dart
diff --git a/pkg/front_end/testcases/inference/generic_methods_downwards_inference_fold.dart b/pkg/front_end/testcases/inference/generic_methods_downwards_inference_fold.dart
index b90360cb14879f7a81177b257213f645d00dfbf6..49edbd4ce9032d6c50908fe6ce891d3b3a3d7ece 100644
--- a/pkg/front_end/testcases/inference/generic_methods_downwards_inference_fold.dart
+++ b/pkg/front_end/testcases/inference/generic_methods_downwards_inference_fold.dart
@@ -5,15 +5,15 @@
 /*@testedFeatures=inference*/
 library test;
 
-void main() {
+void test() {
   List<int> o;
-  int y = o. /*@typeArgs=int*/ /*@target=List::fold*/ fold(
+  int y = o. /*@typeArgs=int*/ /*@target=Iterable::fold*/ fold(
       0,
       /*@returnType=int*/ (/*@type=int*/ x,
               /*@type=int*/ y) =>
           x /*@target=num::+*/ + y);
   var /*@type=dynamic*/ z =
-      o. /*@typeArgs=dynamic*/ /*@target=List::fold*/ fold(
+      o. /*@typeArgs=dynamic*/ /*@target=Iterable::fold*/ fold(
           0,
           /*@returnType=dynamic*/ (/*@type=dynamic*/ x,
               /*@type=int*/ y) => /*info:DYNAMIC_INVOKE*/ x + y);
@@ -22,15 +22,17 @@ void main() {
 
 void functionExpressionInvocation() {
   List<int> o;
-  int y = (o. /*@target=List::fold*/ fold) /*@typeArgs=int*/ (
+  int y = (o. /*@target=Iterable::fold*/ fold) /*@typeArgs=int*/ (
       0,
       /*@returnType=int*/ (/*@type=int*/ x,
               /*@type=int*/ y) =>
           x /*@target=num::+*/ + y);
   var /*@type=dynamic*/ z =
-      (o. /*@target=List::fold*/ fold) /*@typeArgs=dynamic*/ (
+      (o. /*@target=Iterable::fold*/ fold) /*@typeArgs=dynamic*/ (
           0,
           /*@returnType=dynamic*/ (/*@type=dynamic*/ x,
               /*@type=int*/ y) => /*info:DYNAMIC_INVOKE*/ x + y);
   y = /*info:DYNAMIC_CAST*/ z;
 }
+
+main() {}