[Offline Pages] Adds Rappor metrics measuring what domains are saved & viewed.

components/offline_pages/offline_page_model.h

Index: components/offline_pages/offline_page_model.h
diff --git a/components/offline_pages/offline_page_model.h b/components/offline_pages/offline_page_model.h
index 5f5ff65ac6ac89ba3820238889f754802b3b0cba..6790858e95673d691a0103642bf597d5f9312694 100644
--- a/components/offline_pages/offline_page_model.h
+++ b/components/offline_pages/offline_page_model.h
@@ -35,6 +35,9 @@ class Time;
 class TimeDelta;
 class TimeTicks;
 }
+namespace rappor {
+class RapporService;
+}
 
 namespace offline_pages {
 
@@ -109,6 +112,7 @@ class OfflinePageModel : public KeyedService,
   // All blocking calls/disk access will happen on the provided |task_runner|.
   OfflinePageModel(std::unique_ptr<OfflinePageMetadataStore> store,
                    const base::FilePath& archives_dir,
+                   base::WeakPtr<rappor::RapporService> rappor_service,
                    const scoped_refptr<base::SequencedTaskRunner>& task_runner);
   ~OfflinePageModel() override;
 
@@ -367,6 +371,8 @@ class OfflinePageModel : public KeyedService,
   // automatic page clearing.
   std::unique_ptr<OfflinePageStorageManager> storage_manager_;
 
+  base::WeakPtr<rappor::RapporService> rappor_service_;
+
   base::WeakPtrFactory<OfflinePageModel> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(OfflinePageModel);