Add pause/resume functionality to precache

components/precache/content/precache_manager.h

Index: components/precache/content/precache_manager.h
diff --git a/components/precache/content/precache_manager.h b/components/precache/content/precache_manager.h
index dde145a3040f74b5c32b115d0b4c88ef79d926d9..6cbaf7a858ab8dadc5a77f2369f9894e95c9235c 100644
--- a/components/precache/content/precache_manager.h
+++ b/components/precache/content/precache_manager.h
@@ -61,7 +61,9 @@ class PrecacheManager : public KeyedService,
 
   PrecacheManager(content::BrowserContext* browser_context,
                   const sync_driver::SyncService* const sync_service,
-                  const history::HistoryService* const history_service);
+                  const history::HistoryService* const history_service,
+                  std::unique_ptr<PrecacheDatabase> precache_database,
+                  const base::FilePath& db_path);
   ~PrecacheManager() override;
 
   // Returns true if the client is in the experiment group -- that is,
@@ -117,9 +119,16 @@ class PrecacheManager : public KeyedService,
   // From PrecacheFetcher::PrecacheDelegate.
   void OnDone() override;
 
+  // Callback when fetching unfinished work from storage is done.
+  void OnGetUnfinishedWorkDone(
+      std::unique_ptr<PrecacheUnfinishedWork> unfinished_work);
+
   // From history::HistoryService::TopHosts.
   void OnHostsReceived(const history::TopHostsList& host_counts);
 
+  // Initializes and Starts a PrecacheFetcher with unfinished work.
+  void InitializeAndStartFetcher();
+
   // From history::HistoryService::TopHosts. Used for the control group, which
   // gets the list of TopHosts for metrics purposes, but otherwise does nothing.
   void OnHostsReceivedThenDone(const history::TopHostsList& host_counts);
@@ -162,6 +171,9 @@ class PrecacheManager : public KeyedService,
   // Flag indicating whether or not precaching is currently in progress.
   bool is_precaching_;
 
+  // Work that hasn't yet finished.
+  std::unique_ptr<PrecacheUnfinishedWork> unfinished_work_;
+
   DISALLOW_COPY_AND_ASSIGN(PrecacheManager);
 };