[Offline Pages] Add a GCMAppHandler for offline page prefetch.

chrome/browser/BUILD.gn

Index: chrome/browser/BUILD.gn
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 7983299161f22405771f3a92f42b988187d495ee..19a4bb3bfdfca7f7ea5c822fa00f5631af3612d8 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -1514,7 +1514,6 @@ split_static_library("browser") {
     "//components/ntp_snippets",
     "//components/ntp_tiles",
     "//components/offline_items_collection/core",
-    "//components/offline_pages/content",
     "//components/offline_pages/content/background_loader",
     "//components/offline_pages/core",
     "//components/offline_pages/core/background:background_offliner",
@@ -2898,6 +2897,10 @@ split_static_library("browser") {
       "android/offline_pages/offliner_helper.h",
       "android/offline_pages/prefetch/prefetch_background_task.cc",
       "android/offline_pages/prefetch/prefetch_background_task.h",
+      "android/offline_pages/prefetch/prefetch_service_factory.cc",
+      "android/offline_pages/prefetch/prefetch_service_factory.h",
+      "android/offline_pages/prefetch/suggested_articles_observer.cc",
+      "android/offline_pages/prefetch/suggested_articles_observer.h",
       "android/offline_pages/prerender_adapter.cc",
       "android/offline_pages/prerender_adapter.h",
       "android/offline_pages/prerendering_loader.cc",