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

This does not yet react to such messages but hooks up the plumbing so that we are ready for them

Because the app handlers need to be registered before any GCM messages are received, this app handler is added upon construction of the GCMProfileService.

BUG=701939

Review-Url: https://codereview.chromium.org/2864293003
Cr-Commit-Position: refs/heads/master@{#475735}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 057e884..d4ed886 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -2182,6 +2182,8 @@
       "android/offline_pages/request_coordinator_factory.h",
       "offline_pages/background_loader_offliner.cc",
       "offline_pages/background_loader_offliner.h",
+      "offline_pages/prefetch/prefetch_service_factory.cc",
+      "offline_pages/prefetch/prefetch_service_factory.h",
     ]
     if (is_android) {
       sources += [
@@ -2190,7 +2192,6 @@
       ]
     }
     deps += [
-      "//components/offline_pages/content",
       "//components/offline_pages/content/background_loader",
       "//components/offline_pages/core",
       "//components/offline_pages/core/background:background_offliner",