Implementing recent pages snapshot capture.

components/offline_pages/snapshot_controller.h

Index: components/offline_pages/snapshot_controller.h
diff --git a/components/offline_pages/snapshot_controller.h b/components/offline_pages/snapshot_controller.h
index 37f549c609339a05478bbda0c580a3ce2b66a71c..540468718950d3fe440c97876ce40768c2e171b3 100644
--- a/components/offline_pages/snapshot_controller.h
+++ b/components/offline_pages/snapshot_controller.h
@@ -21,6 +21,8 @@ namespace offline_pages {
 //   the new attempts to start a snapshot are ignored until it does.
 // - Some signals prevent more snapshots to be taken.
 //   OnLoad is currently such signal.
+// - Once Reset() is called on the SnapshotController, the delayed tasks are
+//   reset so no StartSnapshot calls is made 'cross-session'.
 class SnapshotController {
  public:
   // kStateReady - listening to input, will start snapshot when needed.
@@ -36,8 +38,7 @@ class SnapshotController {
     // PreviousSnapshotCompleted() before the next StatrSnapshot().
     // Client should overwrite the result of previous snapshot with the new one,
     // it is assumed that later snapshots are better then previous.
-    // Returns true if the snapshot actually started.
-    virtual bool StartSnapshot() = 0;
+    virtual void StartSnapshot() = 0;
 
    protected:
     virtual ~Client() {}
@@ -69,12 +70,15 @@ class SnapshotController {
   size_t GetDelayAfterDocumentAvailableForTest();
 
  private:
-  void MaybeStartSnapshot();
+  void MaybeStartSnapshot(size_t session_id);
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
   // Client owns this class.
   SnapshotController::Client* client_;
   SnapshotController::State state_;
+  // Session counter. Used to check and ignore the delayed tasks from past
+  // sessions.
+  size_t session_counter_;
 
   base::WeakPtrFactory<SnapshotController> weak_ptr_factory_;