[Offline pages] Refactoring helper classes out from offline_page_model_unittest.cc

components/offline_pages/BUILD.gn

Index: components/offline_pages/BUILD.gn
diff --git a/components/offline_pages/BUILD.gn b/components/offline_pages/BUILD.gn
index 2884333074911d265c4ae2cc343d8ca6d3d03a9a..b5311a8171376fde685f8da3645234873bcdbb90 100644
--- a/components/offline_pages/BUILD.gn
+++ b/components/offline_pages/BUILD.gn
@@ -36,6 +36,23 @@ static_library("offline_pages") {
   ]
 }
 
+static_library("test_support") {
+  testonly = true
+  sources = [
+    "offline_page_test_archiver.cc",
+    "offline_page_test_archiver.h",
+    "offline_page_test_store.cc",
+    "offline_page_test_store.h",
+  ]
+
+  deps = [
+    ":offline_pages",
+    "//base",
+    "//testing/gtest",
+    "//url",
+  ]
+}
+
 source_set("unit_tests") {
   testonly = true
   sources = [
@@ -45,6 +62,7 @@ source_set("unit_tests") {
 
   deps = [
     ":offline_pages",
+    ":test_support",
     "//base",
     "//components/bookmarks/browser",
     "//components/leveldb_proto",