Upstream DocumentTabModelImpl and related classes

chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/DocumentTabModelImpl.java

Index: chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/DocumentTabModelImpl.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/DocumentTabModelImpl.java b/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/DocumentTabModelImpl.java
new file mode 100644
index 0000000000000000000000000000000000000000..1a04499d6ac6baf65b1f2cc3200ae07856a6fc71
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/DocumentTabModelImpl.java
@@ -0,0 +1,903 @@
+// Copyright 2014 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.
+
+package org.chromium.chrome.browser.tabmodel.document;
+
+import android.annotation.TargetApi;
+import android.app.Activity;
+import android.content.Context;
+import android.content.Intent;
+import android.content.SharedPreferences;
+import android.os.AsyncTask;
+import android.os.Build;
+import android.text.TextUtils;
+import android.util.Log;
+import android.util.Pair;
+import android.util.SparseArray;
+
+import com.google.protobuf.nano.MessageNano;
+
+import org.chromium.base.ApplicationStatus;
+import org.chromium.base.ObserverList;
+import org.chromium.base.ThreadUtils;
+import org.chromium.base.VisibleForTesting;
+import org.chromium.chrome.browser.Tab;
+import org.chromium.chrome.browser.TabState;
+import org.chromium.chrome.browser.tabmodel.TabList;
+import org.chromium.chrome.browser.tabmodel.TabModel;
+import org.chromium.chrome.browser.tabmodel.TabModelJniBridge;
+import org.chromium.chrome.browser.tabmodel.TabModelObserver;
+import org.chromium.chrome.browser.tabmodel.TabModelUtils;
+import org.chromium.chrome.browser.tabmodel.document.DocumentTabModelInfo.DocumentEntry;
+import org.chromium.chrome.browser.tabmodel.document.DocumentTabModelInfo.DocumentList;
+import org.chromium.chrome.browser.util.MathUtils;
+
+import java.io.File;
+import java.io.IOException;
+import java.lang.ref.WeakReference;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * Maintains a list of Tabs displayed when Chrome is running in document-mode.
+ */
+@TargetApi(Build.VERSION_CODES.LOLLIPOP)
+public class DocumentTabModelImpl extends TabModelJniBridge implements DocumentTabModel {
+    private static final String TAG = "DocumentTabModel";
+
+    @VisibleForTesting
+    public static final String PREF_PACKAGE = "com.google.android.apps.chrome.document";
+
+    @VisibleForTesting
+    public static final String PREF_LAST_SHOWN_TAB_ID_REGULAR = "last_shown_tab_id.regular";
+
+    public static final String PREF_LAST_SHOWN_TAB_ID_INCOGNITO = "last_shown_tab_id.incognito";
+
+    /** TabModel is uninitialized. */
+    public static final int STATE_UNINITIALIZED = 0;
+
+    /** Begin parsing the tasks from Recents and loading persisted state. */
+    public static final int STATE_READ_RECENT_TASKS_START = 1;
+
+    /** Done parsing the tasks from Recents and loading persisted state. */
+    public static final int STATE_READ_RECENT_TASKS_END = 2;
+
+    /** Begin loading the current/prioritized tab state synchronously. */
+    public static final int STATE_LOAD_CURRENT_TAB_STATE_START = 3;
+
+    /** Finish loading the current/prioritized tab state synchronously. */
+    public static final int STATE_LOAD_CURRENT_TAB_STATE_END = 4;
+
+    /** Begin reading TabStates from storage for background tabs. */
+    public static final int STATE_LOAD_TAB_STATE_BG_START = 5;
+
+    /** Done reading TabStates from storage for background tabs. */
+    public static final int STATE_LOAD_TAB_STATE_BG_END = 6;
+
+    /** Begin deserializing the TabState.  Requires the native library. */
+    public static final int STATE_DESERIALIZE_START = 7;
+
+    /** Done deserializing the TabState. */
+    public static final int STATE_DESERIALIZE_END = 8;
+
+    /** Begin parsing the historical tabs. */
+    public static final int STATE_DETERMINE_HISTORICAL_TABS_START = 9;
+
+    /** Done parsing the historical tabs. */
+    public static final int STATE_DETERMINE_HISTORICAL_TABS_END = 10;
+
+    /** Clean out old TabState files. */
+    public static final int STATE_CLEAN_UP_OBSOLETE_TABS = 11;
+
+    /** TabModel is fully ready to use. */
+    public static final int STATE_FULLY_LOADED = 12;
+
+    /** List of known tabs. */
+    private final ArrayList<Integer> mTabIdList;
+
+    /** Stores an entry for each DocumentActivity that is alive.  Keys are document IDs. */
+    private final SparseArray<Entry> mEntryMap;
+
+    /**
+     * Stores tabIds which have been removed from the ActivityManager while Chrome was not alive.
+     * It is cleared after restoration has been finished.
+     */
+    private final List<Integer> mHistoricalTabs;
+
+    /** Delegate for working with the ActivityManager. */
+    private final ActivityDelegate mActivityDelegate;
+
+    /** Delegate for working with the filesystem. */
+    private final StorageDelegate mStorageDelegate;
+
+    /** Delegate that provides Tabs to the DocumentTabModel. */
+    private final TabDelegate mTabDelegate;
+
+    /** ID of a Tab whose state should be loaded immediately, if it belongs to this TabList. */
+    private final int mPrioritizedTabId;
+
+    /** List of observers watching for a particular loading state. */
+    private final ObserverList<InitializationObserver> mInitializationObservers;
+
+    /** List of observers watching the TabModel. */
+    private final ObserverList<TabModelObserver> mObservers;
+
+    /** Context to use. */
+    private final Context mContext;
+
+    /** Current loading status. */
+    private int mCurrentState;
+
+    /** ID of the last tab that was shown to the user. */
+    private int mLastShownTabId = Tab.INVALID_TAB_ID;
+
+    /**
+     * Construct a DocumentTabModelImpl.
+     * @param activityDelegate Used to interact with DocumentActivities.
+     * @param tabDelegate Used to create/get Tabs.
+     * @param isIncognito Whether or not the TabList is managing incognito tabs.
+     * @param prioritizedTabId ID of the tab to prioritize when loading.
+     */
+    public DocumentTabModelImpl(ActivityDelegate activityDelegate, TabDelegate tabDelegate,
+            boolean isIncognito, int prioritizedTabId) {
+        this(activityDelegate, new StorageDelegate(isIncognito), tabDelegate, isIncognito,
+                prioritizedTabId, ApplicationStatus.getApplicationContext());
+    }
+
+    /**
+     * Construct a DocumentTabModel.
+     * @param activityDelegate Delegate to use for accessing the ActivityManager.
+     * @param storageDelegate Delegate to use for accessing persistent storage.
+     * @param tabDelegate Used to create/get Tabs.
+     * @param isIncognito Whether or not the TabList is managing incognito tabs.
+     * @param prioritizedTabId ID of the tab to prioritize when loading.
+     * @param context Context to use for accessing SharedPreferences.
+     *
+     * TODO(dfalcantara): Reduce visibility once DocumentMigrationHelper is upstreamed.
+     */
+    public DocumentTabModelImpl(ActivityDelegate activityDelegate, StorageDelegate storageDelegate,
+            TabDelegate tabDelegate, boolean isIncognito, int prioritizedTabId, Context context) {
+        super(isIncognito);
+        mActivityDelegate = activityDelegate;
+        mStorageDelegate = storageDelegate;
+        mTabDelegate = tabDelegate;
+        mPrioritizedTabId = prioritizedTabId;
+        mContext = context;
+
+        mCurrentState = STATE_UNINITIALIZED;
+        mTabIdList = new ArrayList<Integer>();
+        mEntryMap = new SparseArray<Entry>();
+        mHistoricalTabs = new ArrayList<Integer>();
+        mInitializationObservers = new ObserverList<InitializationObserver>();
+        mObservers = new ObserverList<TabModelObserver>();
+
+        SharedPreferences prefs = mContext.getSharedPreferences(PREF_PACKAGE, Context.MODE_PRIVATE);
+        mLastShownTabId = prefs.getInt(
+                isIncognito() ? PREF_LAST_SHOWN_TAB_ID_INCOGNITO : PREF_LAST_SHOWN_TAB_ID_REGULAR,
+                Tab.INVALID_TAB_ID);
+
+        initializeTabList();
+    }
+
+    @Override
+    public void initializeNative() {
+        if (!isNativeInitialized()) super.initializeNative();
+        deserializeTabStatesAsync();
+    }
+
+    public StorageDelegate getStorageDelegate() {
+        return mStorageDelegate;
+    }
+
+    /**
+     * Finds the index of the given Tab ID.
+     * @param tabId ID of the Tab to find.
+     * @return Index of the tab, or -1 if it couldn't be found.
+     */
+    private int indexOf(int tabId) {
+        return mTabIdList.indexOf(tabId);
+    }
+
+    @Override
+    public int index() {
+        if (getCount() == 0) return TabList.INVALID_TAB_INDEX;
+        int indexOfLastId = indexOf(mLastShownTabId);
+        if (indexOfLastId != -1) return indexOfLastId;
+
+        // The previous Tab is gone; select a Tab based on MRU ordering.
+        List<Entry> tasks = mActivityDelegate.getTasksFromRecents(isIncognito());
+        if (tasks.size() == 0) return TabList.INVALID_TAB_INDEX;
+
+        for (int i = 0; i < tasks.size(); i++) {
+            int lastKnownId = tasks.get(i).tabId;
+            int indexOfMostRecentlyUsedId = indexOf(lastKnownId);
+            if (indexOfMostRecentlyUsedId != -1) return indexOfMostRecentlyUsedId;
+        }
+
+        return TabList.INVALID_TAB_INDEX;
+    }
+
+    @Override
+    public void setLastShownId(int id) {
+        mLastShownTabId = id;
+
+        String prefName =
+                isIncognito() ? PREF_LAST_SHOWN_TAB_ID_INCOGNITO : PREF_LAST_SHOWN_TAB_ID_REGULAR;
+        SharedPreferences prefs = mContext.getSharedPreferences(PREF_PACKAGE, Context.MODE_PRIVATE);
+        SharedPreferences.Editor editor = prefs.edit();
+        editor.putInt(prefName, id);
+        editor.apply();
+    }
+
+    @Override
+    public int indexOf(Tab tab) {
+        if (tab == null) return Tab.INVALID_TAB_ID;
+        return indexOf(tab.getId());
+    }
+
+    @Override
+    public int getCount() {
+        return mTabIdList.size();
+    }
+
+    @Override
+    public boolean isClosurePending(int tabId) {
+        return false;
+    }
+
+    @Override
+    public Tab getTabAt(int index) {
+        if (index < 0 || index >= getCount()) return null;
+
+        // Return a live tab if the corresponding Activity is currently alive.
+        int tabId = mTabIdList.get(index);
+        List<WeakReference<Activity>> activities = ApplicationStatus.getRunningActivities();
+        for (WeakReference<Activity> activityRef : activities) {
+            Tab tab = mTabDelegate.getActivityTab(
+                    isIncognito(), mActivityDelegate, activityRef.get());
+            int documentId = tab == null ? Tab.INVALID_TAB_ID : tab.getId();
+            if (documentId == tabId) return tab;
+        }
+
+        // Try to create a Tab that will hold the Tab's info.
+        Entry entry = mEntryMap.get(tabId);
+        if (entry == null) return null;
+
+        // If a tab has already been initialized, use that.
+        if (entry.placeholderTab != null && entry.placeholderTab.isInitialized()) {
+            return entry.placeholderTab;
+        }
+
+        // Create a frozen Tab if we are capable, or if the previous Tab is just a placeholder.
+        if (entry.tabState != null && isNativeInitialized()
+                && (entry.placeholderTab == null || !entry.placeholderTab.isInitialized())) {
+            entry.placeholderTab = mTabDelegate.createFrozenTab(entry);
+            entry.placeholderTab.initialize();
+        }
+
+        // Create a placeholder Tab that just has the ID.
+        if (entry.placeholderTab == null) {
+            entry.placeholderTab = new Tab(tabId, isIncognito(), null, null);
+        }
+
+        return entry.placeholderTab;
+    }
+
+    @Override
+    public void setIndex(int index, TabSelectionType type) {
+        if (index < 0 || index >= getCount()) return;
+        int tabId = mTabIdList.get(index);
+        mActivityDelegate.moveTaskToFront(isIncognito(), tabId);
+        setLastShownId(tabId);
+    }
+
+    @Override
+    public boolean closeTabAt(int index) {
+        ThreadUtils.assertOnUiThread();
+        if (index < 0 || index >= getCount()) return false;
+
+        int tabId = mTabIdList.get(index);
+        mActivityDelegate.finishAndRemoveTask(isIncognito(), tabId);
+        mTabIdList.remove(index);
+        mEntryMap.remove(tabId);
+        return true;
+    }
+
+    @Override
+    public boolean closeTab(Tab tab) {
+        return closeTab(tab, false, false, false);
+    }
+
+    @Override
+    public boolean closeTab(Tab tabToClose, boolean animate, boolean uponExit, boolean canUndo) {
+        // The tab should be destroyed by the DocumentActivity that owns it.
+        return closeTabAt(indexOf(tabToClose.getId()));
+    }
+
+    @Override
+    protected Tab createTabWithNativeContents(
+            boolean isIncognito, long webContentsPtr, int parentTabId) {
+        mTabDelegate.createTabWithNativeContents(isIncognito, webContentsPtr, parentTabId);
+        return null;
+    }
+
+    @Override
+    protected Tab createNewTabForDevTools(String url) {
+        mTabDelegate.createTabForDevTools(url);
+        return null;
+    }
+
+    @Override
+    protected boolean isSessionRestoreInProgress() {
+        return mCurrentState < STATE_FULLY_LOADED;
+    }
+
+    /**
+     * Add the tab ID to the end of the list.
+     * @param tabId ID to add.
+     */
+    private void addTabId(int tabId) {
+        addTabId(mTabIdList.size(), tabId);
+    }
+
+    /**
+     * Adds the Tab ID at the given index.
+     * @param index Where to add the ID.
+     * @param tabId ID to add.
+     */
+    private void addTabId(int index, int tabId) {
+        if (mTabIdList.contains(tabId)) return;
+        mTabIdList.add(index, tabId);
+    }
+
+    @Override
+    public String getInitialUrlForDocument(int tabId) {
+        Entry entry = mEntryMap.get(tabId);
+        return entry == null ? null : entry.initialUrl;
+    }
+
+    @Override
+    public String getCurrentUrlForDocument(int tabId) {
+        Entry entry = mEntryMap.get(tabId);
+        return entry == null ? null : entry.currentUrl;
+    }
+
+    @Override
+    public boolean isTabStateReady(int tabId) {
+        Entry entry = mEntryMap.get(tabId);
+        return entry == null ? true : entry.isTabStateReady;
+    }
+
+    @Override
+    public TabState getTabStateForDocument(int tabId) {
+        Entry entry = mEntryMap.get(tabId);
+        return entry == null ? null : entry.tabState;
+    }
+
+    @Override
+    public boolean hasEntryForTabId(int tabId) {
+        return mEntryMap.get(tabId) != null;
+    }
+
+    @Override
+    public boolean isRetargetable(int tabId) {
+        Entry entry = mEntryMap.get(tabId);
+        return entry == null ? false : !entry.canGoBack;
+    }
+
+    @Override
+    public void addInitializationObserver(InitializationObserver observer) {
+        ThreadUtils.assertOnUiThread();
+        mInitializationObservers.addObserver(observer);
+    }
+
+    @Override
+    public void updateRecentlyClosed() {
+        ThreadUtils.assertOnUiThread();
+        List<Entry> current = mActivityDelegate.getTasksFromRecents(isIncognito());
+        Set<Integer> removed = new HashSet<Integer>();
+        for (int i = 0; i < mEntryMap.size(); i++) {
+            int tabId = mEntryMap.keyAt(i);
+            if (!isTabIdInEntryList(current, tabId)) {
+                Entry entry = mEntryMap.get(tabId);
+                if (!isIncognito() && entry.tabState != null
+                        && entry.tabState.contentsState != null) {
+                    entry.tabState.contentsState.createHistoricalTab();
+                }
+                removed.add(tabId);
+            }
+        }
+
+        for (Integer tabId : removed) {
+            closeTabAt(indexOf(tabId));
+        }
+    }
+
+    @Override
+    public void updateEntry(Intent intent, Tab tab) {
+        if (!mActivityDelegate.isValidActivity(isIncognito(), intent)) return;
+
+        int id = ActivityDelegate.getTabIdFromIntent(intent);
+        if (id == Tab.INVALID_TAB_ID) return;
+
+        Entry currentEntry = mEntryMap.get(id);
+        String currentUrl = tab.getUrl();
+        boolean canGoBack = tab.canGoBack();
+        TabState state = tab.getState();
+        if (currentEntry != null
+                && currentEntry.tabId == id
+                && TextUtils.equals(currentEntry.currentUrl, currentUrl)
+                && currentEntry.canGoBack == canGoBack
+                && currentEntry.tabState == state
+                && !tab.isTabStateDirty()) {
+            return;
+        }
+
+        if (currentEntry == null) {
+            currentEntry = new Entry(id, ActivityDelegate.getInitialUrlForDocument(intent));
+            mEntryMap.put(id, currentEntry);
+        }
+        currentEntry.isDirty = true;
+        currentEntry.currentUrl = currentUrl;
+        currentEntry.canGoBack = canGoBack;
+        currentEntry.tabState = state;
+
+        // TODO(dfalcantara): This is different from how the normal Tab determines when to save its
+        // state, but this can't be fixed because we cann't hold onto Tabs in this class.
+        tab.setIsTabStateDirty(false);
+
+        if (currentEntry.placeholderTab != null) {
+            if (currentEntry.placeholderTab.isInitialized()) currentEntry.placeholderTab.destroy();
+            currentEntry.placeholderTab = null;
+        }
+
+        writeGeneralDataToStorageAsync();
+        writeTabStatesToStorageAsync();
+    }
+
+    @Override
+    public int getCurrentInitializationStage() {
+        return mCurrentState;
+    }
+
+    /**
+     * Add an entry to the entry map for migration purposes.
+     * @param entry The entry to be added.
+     *
+     * TODO(dfalcantara): Reduce visibility once DocumentMigrationHelper is upstreamed.
+     */
+    public void addEntryForMigration(Entry entry) {
+        addTabId(getCount(), entry.tabId);
+        if (mEntryMap.indexOfKey(entry.tabId) >= 0) return;
+        mEntryMap.put(entry.tabId, entry);
+    }
+
+    private void initializeTabList() {
+        setCurrentState(STATE_READ_RECENT_TASKS_START);
+
+        // Run through Recents to see what tasks exist. Prevent them from being retargeted until we
+        // have had the opportunity to load more information about them.
+        List<Entry> entries = mActivityDelegate.getTasksFromRecents(isIncognito());
+        for (Entry entry : entries) {
+            entry.canGoBack = true;
+            mEntryMap.put(entry.tabId, entry);
+        }
+
+        // Read the file, which saved out the task IDs in regular order.
+        byte[] tabFileBytes = mStorageDelegate.readTaskFileBytes();
+        if (tabFileBytes != null) {
+            try {
+                DocumentList list = MessageNano.mergeFrom(new DocumentList(), tabFileBytes);
+                for (int i = 0; i < list.entries.length; i++) {
+                    DocumentEntry savedEntry = list.entries[i];
+                    int tabId = savedEntry.tabId;
+
+                    if (mEntryMap.indexOfKey(tabId) < 0) {
+                        mHistoricalTabs.add(tabId);
+                        continue;
+                    }
+
+                    addTabId(getCount(), tabId);
+                    mEntryMap.get(tabId).canGoBack = savedEntry.canGoBack;
+                }
+            } catch (IOException e) {
+                Log.e(TAG, "I/O exception", e);
+            }
+        }
+
+        // Add any missing tasks to the list.
+        for (int i = 0; i < mEntryMap.size(); i++) {
+            int id = mEntryMap.keyAt(i);
+            if (mTabIdList.contains(id)) continue;
+            addTabId(id);
+        }
+
+        setCurrentState(STATE_READ_RECENT_TASKS_END);
+    }
+
+    // TODO(mariakhomenko): we no longer need prioritized tab id in constructor, shift it here.
+    @Override
+    public void startTabStateLoad() {
+        if (mCurrentState != STATE_READ_RECENT_TASKS_END) return;
+        setCurrentState(STATE_LOAD_CURRENT_TAB_STATE_START);
+        // Immediately try loading the requested tab.
+        if (mPrioritizedTabId != Tab.INVALID_TAB_ID) {
+            Entry entry = mEntryMap.get(mPrioritizedTabId);
+            if (entry != null) {
+                entry.tabState = mStorageDelegate.restoreTabState(mPrioritizedTabId);
+                entry.isTabStateReady = true;
+            }
+        }
+        setCurrentState(STATE_LOAD_CURRENT_TAB_STATE_END);
+        loadTabStatesAsync();
+    }
+
+    private void loadTabStatesAsync() {
+        new AsyncTask<Void, Void, Void>() {
+            private final List<Entry> mEntries = new ArrayList<Entry>(getCount());
+
+            @Override
+            public void onPreExecute() {
+                setCurrentState(STATE_LOAD_TAB_STATE_BG_START);
+                for (int i = 0; i < getCount(); i++) {
+                    mEntries.add(new Entry(getTabAt(i).getId()));
+                }
+            }
+
+            @Override
+            public Void doInBackground(Void... params) {
+                for (Entry entry : mEntries) {
+                    if (mPrioritizedTabId == entry.tabId) continue;
+                    entry.tabState = mStorageDelegate.restoreTabState(entry.tabId);
+                    entry.isTabStateReady = true;
+                }
+
+                return null;
+            }
+
+            @Override
+            public void onPostExecute(Void result) {
+                for (Entry pair : mEntries) {
+                    Entry entry = mEntryMap.get(pair.tabId);
+                    if (entry == null) continue;
+
+                    if (entry.tabState == null) entry.tabState = pair.tabState;
+                    entry.isTabStateReady = true;
+                }
+
+                setCurrentState(STATE_LOAD_TAB_STATE_BG_END);
+                deserializeTabStatesAsync();
+            }
+        }.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR);
+    }
+
+    private void deserializeTabStatesAsync() {
+        if (!shouldStartDeserialization(mCurrentState)) return;
+
+        new AsyncTask<Void, Void, Void>() {
+            private final List<Entry> mCachedEntries = new ArrayList<Entry>(mEntryMap.size());
+
+            @Override
+            public void onPreExecute() {
+                setCurrentState(STATE_DESERIALIZE_START);
+
+                for (int i = 0; i < mEntryMap.size(); i++) {
+                    Entry entry = mEntryMap.valueAt(i);
+                    if (entry.tabState == null) continue;
+                    mCachedEntries.add(new Entry(entry.tabId, entry.tabState));
+                }
+            }
+
+            @Override
+            public Void doInBackground(Void... params) {
+                for (Entry entry : mCachedEntries) {
+                    TabState tabState = entry.tabState;
+                    updateEntryInfoFromTabState(entry, tabState);
+                }
+                return null;
+            }
+
+            @Override
+            public void onPostExecute(Void result) {
+                for (Entry pair : mCachedEntries) {
+                    Entry realEntry = mEntryMap.get(pair.tabId);
+                    if (realEntry == null || realEntry.currentUrl != null) continue;
+                    realEntry.currentUrl = pair.currentUrl;
+                }
+
+                setCurrentState(STATE_DESERIALIZE_END);
+                if (isNativeInitialized()) {
+                    broadcastSessionRestoreComplete();
+                    loadHistoricalTabsAsync();
+                }
+            }
+        }.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR);
+    }
+
+    /**
+     * Call for extending classes to override for getting additional information for an entry from
+     * the tab state when it is deserialized.
+     * @param entry The {@link Entry} currently being processed
+     * @param tabState The {@link TabState} that has been deserialized for the entry.
+     */
+    protected void updateEntryInfoFromTabState(Entry entry, TabState tabState) {
+        entry.currentUrl = tabState.getVirtualUrlFromState();
+    }
+
+    /**
+     * Checks whether initialization should move to the deserialization step.
+     * @param currentState Current initialization stage.
+     * @return Whether to proceed or not.
+     */
+    protected boolean shouldStartDeserialization(int currentState) {
+        return isNativeInitialized() && currentState == STATE_LOAD_TAB_STATE_BG_END;
+    }
+
+    private void loadHistoricalTabsAsync() {
+        new AsyncTask<Void, Void, Void>() {
+            private Set<Integer> mHistoricalTabsForBackgroundThread;
+            private List<Entry> mEntries;
+
+            @Override
+            public void onPreExecute() {
+                setCurrentState(STATE_DETERMINE_HISTORICAL_TABS_START);
+                mHistoricalTabsForBackgroundThread = new HashSet<Integer>(mHistoricalTabs.size());
+                mHistoricalTabsForBackgroundThread.addAll(mHistoricalTabs);
+                mEntries = new ArrayList<Entry>(mHistoricalTabsForBackgroundThread.size());
+            }
+
+            @Override
+            public Void doInBackground(Void... params) {
+                for (Integer tabId : mHistoricalTabsForBackgroundThread) {
+                    // Read the saved state, then delete the file.
+                    TabState state = mStorageDelegate.restoreTabState(tabId);
+                    mEntries.add(new Entry(tabId, state));
+                    mStorageDelegate.deleteTabStateFile(tabId);
+                }
+
+                return null;
+            }
+
+            @Override
+            public void onPostExecute(Void result) {
+                for (Entry entry : mEntries) {
+                    if (entry.tabState == null || entry.tabState.contentsState == null) continue;
+                    entry.tabState.contentsState.createHistoricalTab();
+                }
+                mHistoricalTabs.clear();
+                setCurrentState(STATE_DETERMINE_HISTORICAL_TABS_END);
+                cleanUpObsoleteTabStatesAsync();
+            }
+        }.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR);
+    }
+
+    /**
+     * Clears the folder of TabStates that correspond to missing tasks.
+     */
+    private void cleanUpObsoleteTabStatesAsync() {
+        new AsyncTask<Void, Void, Void>() {
+            private List<Entry> mCurrentTabs;
+
+            @Override
+            protected void onPreExecute() {
+                setCurrentState(STATE_CLEAN_UP_OBSOLETE_TABS);
+                mCurrentTabs = mActivityDelegate.getTasksFromRecents(isIncognito());
+            }
+
+            @Override
+            protected Void doInBackground(Void... voids) {
+                File stateDirectory = mStorageDelegate.getStateDirectory();
+                String[] files = stateDirectory.list();
+                for (final String fileName : files) {
+                    Pair<Integer, Boolean> tabInfo = TabState.parseInfoFromFilename(fileName);
+                    if (tabInfo == null) continue;
+
+                    int tabId = tabInfo.first;
+                    boolean incognito = tabInfo.second;
+                    if (incognito != isIncognito() || isTabIdInEntryList(mCurrentTabs, tabId)) {
+                        continue;
+                    }
+
+                    boolean success = new File(stateDirectory, fileName).delete();
+                    if (!success) Log.w(TAG, "Failed to delete: " + fileName);
+                }
+
+                return null;
+            }
+
+            @Override
+            protected void onPostExecute(Void result) {
+                setCurrentState(STATE_FULLY_LOADED);
+            }
+        }.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR);
+    }
+
+    /**
+     * Save out a tiny file with minimal information required for retargeting.
+     */
+    private void writeGeneralDataToStorageAsync() {
+        if (isIncognito()) return;
+
+        new AsyncTask<Void, Void, Void>() {
+            private DocumentList mList;
+
+            @Override
+            protected void onPreExecute() {
+                List<DocumentEntry> entriesList = new ArrayList<DocumentEntry>();
+                for (int i = 0; i < getCount(); i++) {
+                    Entry entry = mEntryMap.get(getTabAt(i).getId());
+                    if (entry == null) continue;
+
+                    DocumentEntry docEntry = new DocumentEntry();
+                    docEntry.tabId = entry.tabId;
+                    docEntry.canGoBack = entry.canGoBack;
+
+                    entriesList.add(docEntry);
+                }
+                mList = new DocumentList();
+                mList.entries = entriesList.toArray(new DocumentEntry[entriesList.size()]);
+            }
+
+            @Override
+            protected Void doInBackground(Void... params) {
+                mStorageDelegate.writeTaskFileBytes(MessageNano.toByteArray(mList));
+                return null;
+            }
+        }.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR);
+    }
+
+    /**
+     * Write out all of the TabStates.
+     */
+    private void writeTabStatesToStorageAsync() {
+        new AsyncTask<Void, Void, Void>() {
+            private final SparseArray<TabState> mStatesToWrite = new SparseArray<TabState>();
+
+            @Override
+            protected void onPreExecute() {
+                for (int i = 0; i < mEntryMap.size(); i++) {
+                    Entry entry = mEntryMap.valueAt(i);
+                    if (!entry.isDirty || entry.tabState == null) continue;
+                    mStatesToWrite.put(entry.tabId, entry.tabState);
+                }
+            }
+
+            @Override
+            protected Void doInBackground(Void... voids) {
+                for (int i = 0; i < mStatesToWrite.size(); i++) {
+                    int tabId = mStatesToWrite.keyAt(i);
+                    mStorageDelegate.saveTabState(tabId, mStatesToWrite.valueAt(i));
+                }
+                return null;
+            }
+
+            @Override
+            protected void onPostExecute(Void v) {
+                for (int i = 0; i < mStatesToWrite.size(); i++) {
+                    int tabId = mStatesToWrite.keyAt(i);
+                    Entry entry = mEntryMap.get(tabId);
+                    if (entry == null) continue;
+                    entry.isDirty = false;
+                }
+            }
+        }.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR);
+    }
+
+    private void setCurrentState(int newState) {
+        ThreadUtils.assertOnUiThread();
+        assert mCurrentState == newState - 1;
+        mCurrentState = newState;
+
+        for (InitializationObserver observer : mInitializationObservers) {
+            if (observer.isCanceled()) {
+                Log.w(TAG, "Observer alerted after canceled: " + observer);
+                mInitializationObservers.removeObserver(observer);
+            } else if (observer.isSatisfied(mCurrentState)) {
+                observer.runWhenReady();
+                mInitializationObservers.removeObserver(observer);
+            }
+        }
+    }
+
+    @Override
+    public Tab getNextTabIfClosed(int id) {
+        // Tab may not necessarily exist.
+        return null;
+    }
+
+    @Override
+    public void closeAllTabs() {
+        closeAllTabs(true, false);
+    }
+
+    @Override
+    public void closeAllTabs(boolean allowDelegation, boolean uponExit) {
+        for (int i = getCount() - 1; i >= 0; i--) closeTabAt(i);
+    }
+
+    @Override
+    public void moveTab(int id, int newIndex) {
+        newIndex = MathUtils.clamp(newIndex, 0, getCount());
+        int curIndex = TabModelUtils.getTabIndexById(this, id);
+        if (curIndex == INVALID_TAB_INDEX || curIndex == newIndex || curIndex + 1 == newIndex) {
+            return;
+        }
+
+        mTabIdList.remove(curIndex);
+        addTabId(newIndex, id);
+
+        Tab tab = getTabAt(curIndex);
+        if (tab == null) return;
+        for (TabModelObserver obs : mObservers) obs.didMoveTab(tab, newIndex, curIndex);
+    }
+
+    @Override
+    public void destroy() {
+        super.destroy();
+        mInitializationObservers.clear();
+        mObservers.clear();
+    }
+
+    @Override
+    public void addTab(Tab tab) {
+        int parentIndex = indexOf(tab.getParentId());
+        int index = parentIndex == -1 ? getCount() : parentIndex + 1;
+        addTab(tab, index, tab.getLaunchType());
+    }
+
+    @Override
+    public void addTab(Tab tab, int index, TabLaunchType type) {
+        for (TabModelObserver obs : mObservers) obs.willAddTab(tab, type);
+
+        if (index == TabModel.INVALID_TAB_INDEX) {
+            addTabId(getCount(), tab.getId());
+        } else {
+            addTabId(index, tab.getId());
+        }
+
+        tabAddedToModel(tab);
+        for (TabModelObserver obs : mObservers) obs.didAddTab(tab, type);
+    }
+
+    @Override
+    public boolean supportsPendingClosures() {
+        return false;
+    }
+
+    @Override
+    public void commitAllTabClosures() {
+    }
+
+    @Override
+    public void commitTabClosure(int tabId) {
+    }
+
+    @Override
+    public void cancelTabClosure(int tabId) {
+    }
+
+    @Override
+    public TabList getComprehensiveModel() {
+        return this;
+    }
+
+    @Override
+    public void addObserver(TabModelObserver observer) {
+        mObservers.addObserver(observer);
+    }
+
+    @Override
+    public void removeObserver(TabModelObserver observer) {
+        mObservers.removeObserver(observer);
+    }
+
+    private static boolean isTabIdInEntryList(List<Entry> entries, int tabId) {
+        for (int i = 0; i < entries.size(); i++) {
+            if (entries.get(i).tabId == tabId) return true;
+        }
+        return false;
+    }
+}