Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_item_unittest.cc

Index: components/offline_pages/core/prefetch/prefetch_item_unittest.cc
diff --git a/components/offline_pages/core/prefetch/prefetch_item_unittest.cc b/components/offline_pages/core/prefetch/prefetch_item_unittest.cc
index 68433d477dc3d162b7ae5ce060cfebfcb6964146..e5710ea21259c3dcb06f9de16c04a547a5f77c0d 100644
--- a/components/offline_pages/core/prefetch/prefetch_item_unittest.cc
+++ b/components/offline_pages/core/prefetch/prefetch_item_unittest.cc
@@ -21,12 +21,7 @@ TEST(PrefetchItemTest, OperatorEqualsAndCopyConstructor) {
   EXPECT_EQ(item1, PrefetchItem(item1));
   item1 = PrefetchItem();
 
-  item1.client_name_space = "B";
-  EXPECT_NE(item1, PrefetchItem());
-  EXPECT_EQ(item1, PrefetchItem(item1));
-  item1 = PrefetchItem();
-
-  item1.client_id = "C";
+  item1.client_id = ClientId("B", "C");
   EXPECT_NE(item1, PrefetchItem());
   EXPECT_EQ(item1, PrefetchItem(item1));
   item1 = PrefetchItem();