Implementing recent pages snapshot capture.

components/offline_pages/snapshot_controller.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/offline_pages/snapshot_controller.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/time/time.h"
 
 namespace {
 // Delay, in milliseconds, between the main document parsed event and snapshot.
 // Note if the "load" event fires before this delay is up, then the snapshot
 // is taken immediately.
 const size_t kDelayAfterDocumentAvailable = 7000;
 
 }  // namespace
 
 namespace offline_pages {
 
 SnapshotController::SnapshotController(
     const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
     SnapshotController::Client* client)
     : 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;
 }
 
 void SnapshotController::Stop() {
   state_ = State::kStopped;
 }
 
 void SnapshotController::PendingSnapshotCompleted() {
   // Unless the controller is "stopped", enable the subsequent snapshots.
   // Stopped state prevents any further snapshots form being started.
   if (state_ == State::kStopped)
     return;
   DCHECK(state_ == State::kSnapshotPending);
   state_ = State::kReady;
 }
 
 void SnapshotController::DocumentAvailableInMainFrame() {
   // Post a delayed task. The snapshot will happen either when the delay
   // is up, or if the "load" event is dispatched in the main frame.
   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() {
   return kDelayAfterDocumentAvailable;
 }
 
 
 }  // namespace offline_pages