[Offline pages] Create offliner that uses background loader

components/offline_pages/content/background_loader/BUILD.gn

Index: components/offline_pages/content/background_loader/BUILD.gn
diff --git a/components/offline_pages/content/background_loader/BUILD.gn b/components/offline_pages/content/background_loader/BUILD.gn
index 9e6aaeda9d37ba255c97a8ee690d4433daa34788..b552743994a2e68f6e911affa95d4f00a7a1027d 100644
--- a/components/offline_pages/content/background_loader/BUILD.gn
+++ b/components/offline_pages/content/background_loader/BUILD.gn
@@ -18,6 +18,20 @@ source_set("background_loader") {
   ]
 }
 
+source_set("test_support") {
+  testonly = true
+
+  sources = [
+    "background_loader_contents_stub.cc",
+    "background_loader_contents_stub.h",
+  ]
+
+  deps = [
+    ":background_loader",
+    "//content/test:test_support",
+  ]
+}
+
 source_set("unit_tests") {
   testonly = true
   sources = [