Offline Page Cache uses user interaction triggers for saving pages.

components/offline_pages/core/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/core/snapshot_controller.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/time/time.h"
@@ skipping 35 matching lines @@
       delay_after_document_on_load_completed_ms_(
           delay_after_document_on_load_completed_ms),
       weak_ptr_factory_(this) {}
 
 SnapshotController::~SnapshotController() {}
 
 void SnapshotController::Reset() {
   // Cancel potentially delayed tasks that relate to the previous 'session'.
   weak_ptr_factory_.InvalidateWeakPtrs();
   state_ = State::READY;
+  current_page_quality_ = PageQuality::POOR;
 }
 
 void SnapshotController::Stop() {
   state_ = State::STOPPED;
 }
 
 void SnapshotController::PendingSnapshotCompleted() {
   // Unless the controller is "stopped", enable the subsequent snapshots.
   // Stopped state prevents any further snapshots form being started.
   if (state_ == State::STOPPED)
     return;
   state_ = State::READY;
 }
 
 void SnapshotController::DocumentAvailableInMainFrame() {
+  DCHECK_EQ(PageQuality::POOR, current_page_quality_);
   // Post a delayed task to snapshot.
   task_runner_->PostDelayedTask(
       FROM_HERE, base::Bind(&SnapshotController::MaybeStartSnapshot,
-                            weak_ptr_factory_.GetWeakPtr()),
+                            weak_ptr_factory_.GetWeakPtr(),
+                            PageQuality::FAIR_AND_IMPROVING),
       base::TimeDelta::FromMilliseconds(delay_after_document_available_ms_));
 }
 
 void SnapshotController::DocumentOnLoadCompletedInMainFrame() {
   // Post a delayed task to snapshot and then stop this controller.
   task_runner_->PostDelayedTask(
       FROM_HERE, base::Bind(&SnapshotController::MaybeStartSnapshotThenStop,
                             weak_ptr_factory_.GetWeakPtr()),
       base::TimeDelta::FromMilliseconds(
           delay_after_document_on_load_completed_ms_));
 }
 
-void SnapshotController::MaybeStartSnapshot() {
+void SnapshotController::MaybeStartSnapshot(PageQuality updated_page_quality) {
   if (state_ != State::READY)
     return;
+  DCHECK_LT(current_page_quality_, updated_page_quality);
+  current_page_quality_ = updated_page_quality;
   state_ = State::SNAPSHOT_PENDING;
   client_->StartSnapshot();
 }
 
 void SnapshotController::MaybeStartSnapshotThenStop() {
-  MaybeStartSnapshot();
+  MaybeStartSnapshot(PageQuality::HIGH);
   Stop();
 }
 
 size_t SnapshotController::GetDelayAfterDocumentAvailableForTest() {
   return delay_after_document_available_ms_;
 }
 
 size_t SnapshotController::GetDelayAfterDocumentOnLoadCompletedForTest() {
   return delay_after_document_on_load_completed_ms_;
 }
 
 }  // namespace offline_pages