Implementing recent pages snapshot capture.

components/offline_pages/snapshot_controller.cc

Index: components/offline_pages/snapshot_controller.cc
diff --git a/components/offline_pages/snapshot_controller.cc b/components/offline_pages/snapshot_controller.cc
index b086e486c34a505e5adbfb7711486d462f9ea652..247e193161889d6dba16dc33836bfe9b103e13db 100644
--- a/components/offline_pages/snapshot_controller.cc
+++ b/components/offline_pages/snapshot_controller.cc
@@ -25,12 +25,14 @@ SnapshotController::SnapshotController(
     : task_runner_(task_runner),
       client_(client),
       state_(State::kReady),
+      session_counter_(0),
       weak_ptr_factory_(this) {
 }
 
 SnapshotController::~SnapshotController() {}
 
 void SnapshotController::Reset() {
+  session_counter_++;
   state_ = State::kReady;
 }
 
@@ -53,22 +55,26 @@ void SnapshotController::DocumentAvailableInMainFrame() {
   task_runner_->PostDelayedTask(
       FROM_HERE,
       base::Bind(&SnapshotController::MaybeStartSnapshot,
-                 weak_ptr_factory_.GetWeakPtr()),
+                 weak_ptr_factory_.GetWeakPtr(),
+                 session_counter_),
       base::TimeDelta::FromMilliseconds(kDelayAfterDocumentAvailable));
 }
 
 void SnapshotController::DocumentOnLoadCompletedInMainFrame() {
-  MaybeStartSnapshot();
+  MaybeStartSnapshot(session_counter_);
   // No more snapshots after onLoad (there still can be other events
   // or delayed tasks that can try to start another snapshot)
   Stop();
 }
 
-void SnapshotController::MaybeStartSnapshot() {
+void SnapshotController::MaybeStartSnapshot(size_t session_id) {
   if (state_ != State::kReady)
     return;
-  if (client_->StartSnapshot())
-    state_ = State::kSnapshotPending;
+  // This task was posted for previous session, ignore it.
+  if (session_id != session_counter_)
+    return;
+  state_ = State::kSnapshotPending;
+  client_->StartSnapshot();
 }
 
 size_t SnapshotController::GetDelayAfterDocumentAvailableForTest() {