Refactoring of SessionService to get componentized.

chrome/browser/sessions/session_service_commands.cc

+// 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.
+
+#include "chrome/browser/sessions/session_service_commands.h"
+
+#include <vector>
+
+#include "base/bind.h"
+#include "base/pickle.h"
+#include "chrome/browser/sessions/base_session_service_delegate.h"
+#include "chrome/browser/sessions/session_backend.h"
+#include "chrome/browser/sessions/session_command.h"
+#include "chrome/browser/sessions/session_types.h"
+#include "components/startup_metric_utils/startup_metric_utils.h"
+
+// Identifier for commands written to file.
+static const SessionCommand::id_type kCommandSetTabWindow = 0;
+// OBSOLETE Superseded by kCommandSetWindowBounds3.
+// static const SessionCommand::id_type kCommandSetWindowBounds = 1;
+static const SessionCommand::id_type kCommandSetTabIndexInWindow = 2;
+static const SessionCommand::id_type
+    kCommandTabNavigationPathPrunedFromBack = 5;
+static const SessionCommand::id_type kCommandUpdateTabNavigation = 6;
+static const SessionCommand::id_type kCommandSetSelectedNavigationIndex = 7;
+static const SessionCommand::id_type kCommandSetSelectedTabInIndex = 8;
+static const SessionCommand::id_type kCommandSetWindowType = 9;
+// OBSOLETE Superseded by kCommandSetWindowBounds3. Except for data migration.
+// static const SessionCommand::id_type kCommandSetWindowBounds2 = 10;
+static const SessionCommand::id_type
+    kCommandTabNavigationPathPrunedFromFront = 11;
+static const SessionCommand::id_type kCommandSetPinnedState = 12;
+static const SessionCommand::id_type kCommandSetExtensionAppID = 13;
+static const SessionCommand::id_type kCommandSetWindowBounds3 = 14;
+static const SessionCommand::id_type kCommandSetWindowAppName = 15;
+static const SessionCommand::id_type kCommandTabClosed = 16;
+static const SessionCommand::id_type kCommandWindowClosed = 17;
+static const SessionCommand::id_type kCommandSetTabUserAgentOverride = 18;
+static const SessionCommand::id_type kCommandSessionStorageAssociated = 19;
+static const SessionCommand::id_type kCommandSetActiveWindow = 20;
+
+// Every kWritesPerReset commands triggers recreating the file.
+static const int kWritesPerReset = 250;
+
+namespace {
+
+// Various payload structures.
+struct ClosedPayload {
+  SessionID::id_type id;
+  int64 close_time;
+};
+
+struct WindowBoundsPayload2 {
+  SessionID::id_type window_id;
+  int32 x;
+  int32 y;
+  int32 w;
+  int32 h;
+  bool is_maximized;
+};
+
+struct WindowBoundsPayload3 {
+  SessionID::id_type window_id;
+  int32 x;
+  int32 y;
+  int32 w;
+  int32 h;
+  int32 show_state;
+};
+
+typedef SessionID::id_type ActiveWindowPayload;
+
+struct IDAndIndexPayload {
+  SessionID::id_type id;
+  int32 index;
+};
+
+typedef IDAndIndexPayload TabIndexInWindowPayload;
+
+typedef IDAndIndexPayload TabNavigationPathPrunedFromBackPayload;
+
+typedef IDAndIndexPayload SelectedNavigationIndexPayload;
+
+typedef IDAndIndexPayload SelectedTabInIndexPayload;
+
+typedef IDAndIndexPayload WindowTypePayload;
+
+typedef IDAndIndexPayload TabNavigationPathPrunedFromFrontPayload;
+
+struct PinnedStatePayload {
+  SessionID::id_type tab_id;
+  bool pinned_state;
+};
+
+// Persisted versions of ui::WindowShowState that are written to disk and can
+// never change.
+enum PersistedWindowShowState {
+  // SHOW_STATE_DEFAULT (0) never persisted.
+  PERSISTED_SHOW_STATE_NORMAL = 1,
+  PERSISTED_SHOW_STATE_MINIMIZED = 2,
+  PERSISTED_SHOW_STATE_MAXIMIZED = 3,
+  // SHOW_STATE_INACTIVE (4) never persisted.
+  PERSISTED_SHOW_STATE_FULLSCREEN = 5,
+  PERSISTED_SHOW_STATE_DETACHED_DEPRECATED = 6,
+  PERSISTED_SHOW_STATE_END = 6
+};
+
+// Assert to ensure PersistedWindowShowState is updated if ui::WindowShowState
+// is changed.
+COMPILE_ASSERT(ui::SHOW_STATE_END ==
+                   static_cast<ui::WindowShowState>(PERSISTED_SHOW_STATE_END),
+               persisted_show_state_mismatch);
+
+// Returns the show state to store to disk based |state|.
+PersistedWindowShowState ShowStateToPersistedShowState(
+    ui::WindowShowState state) {
+  switch (state) {
+    case ui::SHOW_STATE_NORMAL:
+      return PERSISTED_SHOW_STATE_NORMAL;
+    case ui::SHOW_STATE_MINIMIZED:
+      return PERSISTED_SHOW_STATE_MINIMIZED;
+    case ui::SHOW_STATE_MAXIMIZED:
+      return PERSISTED_SHOW_STATE_MAXIMIZED;
+    case ui::SHOW_STATE_FULLSCREEN:
+      return PERSISTED_SHOW_STATE_FULLSCREEN;
+
+    case ui::SHOW_STATE_DEFAULT:
+    case ui::SHOW_STATE_INACTIVE:
+      return PERSISTED_SHOW_STATE_NORMAL;
+
+    case ui::SHOW_STATE_END:
+      break;
+  }
+  NOTREACHED();
+  return PERSISTED_SHOW_STATE_NORMAL;
+}
+
+// Lints show state values when read back from persited disk.
+ui::WindowShowState PersistedShowStateToShowState(int state) {
+  switch (state) {
+    case PERSISTED_SHOW_STATE_NORMAL:
+      return ui::SHOW_STATE_NORMAL;
+    case PERSISTED_SHOW_STATE_MINIMIZED:
+      return ui::SHOW_STATE_MINIMIZED;
+    case PERSISTED_SHOW_STATE_MAXIMIZED:
+      return ui::SHOW_STATE_MAXIMIZED;
+    case PERSISTED_SHOW_STATE_FULLSCREEN:
+      return ui::SHOW_STATE_FULLSCREEN;
+    case PERSISTED_SHOW_STATE_DETACHED_DEPRECATED:
+      return ui::SHOW_STATE_NORMAL;
+  }
+  NOTREACHED();
+  return ui::SHOW_STATE_NORMAL;
+}
+
+}  // namespace
+
+// SessionService -------------------------------------------------------------
+
+SessionServiceCommands::SessionServiceCommands(
+  BaseSessionService::SessionType type,
+  const base::FilePath& path,
+  scoped_ptr<BaseSessionServiceDelegate> delegate)
+    : BaseSessionService(type, path, delegate.Pass()),
+      weak_factory_(this) {
+}
+
+SessionServiceCommands::~SessionServiceCommands() {
+  // The owner is responsible to save upon exit.
+}
+
+base::CancelableTaskTracker::TaskId SessionServiceCommands::GetLastSession(
+    const SessionCallback& callback,
+    base::CancelableTaskTracker* tracker) {
+  // OnGotSessionServiceCommands maps the SessionServiceCommands to browser state, then run
+  // the callback.
+  return ScheduleGetLastSessionCommands(
+      base::Bind(&SessionServiceCommands::OnGotSessionServiceCommands,
+                 weak_factory_.GetWeakPtr(), callback),
+      tracker);
+}
+
+SessionCommand* SessionServiceCommands::CreateSetSelectedTabInWindow(
+    const SessionID& window_id,
+    int index) {
+  SelectedTabInIndexPayload payload = { 0 };
+  payload.id = window_id.id();
+  payload.index = index;
+  SessionCommand* command = new SessionCommand(kCommandSetSelectedTabInIndex,
+                                 sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateSetTabWindow(
+    const SessionID& window_id,
+    const SessionID& tab_id) {
+  SessionID::id_type payload[] = { window_id.id(), tab_id.id() };
+  SessionCommand* command =
+      new SessionCommand(kCommandSetTabWindow, sizeof(payload));
+  memcpy(command->contents(), payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateSetWindowBounds(
+    const SessionID& window_id,
+    const gfx::Rect& bounds,
+    ui::WindowShowState show_state) {
+  WindowBoundsPayload3 payload = { 0 };
+  payload.window_id = window_id.id();
+  payload.x = bounds.x();
+  payload.y = bounds.y();
+  payload.w = bounds.width();
+  payload.h = bounds.height();
+  payload.show_state = ShowStateToPersistedShowState(show_state);
+  SessionCommand* command = new SessionCommand(kCommandSetWindowBounds3,
+                                               sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateSetTabIndexInWindow(
+    const SessionID& tab_id,
+    int new_index) {
+  TabIndexInWindowPayload payload = { 0 };
+  payload.id = tab_id.id();
+  payload.index = new_index;
+  SessionCommand* command =
+      new SessionCommand(kCommandSetTabIndexInWindow, sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateTabClosed(
+    const SessionID::id_type tab_id) {
+  ClosedPayload payload;
+  // Because of what appears to be a compiler bug setting payload to {0} doesn't
+  // set the padding to 0, resulting in Purify reporting an UMR when we write
+  // the structure to disk. To avoid this we explicitly memset the struct.
+  memset(&payload, 0, sizeof(payload));
+  payload.id = tab_id;
+  payload.close_time = base::Time::Now().ToInternalValue();
+  SessionCommand* command =
+      new SessionCommand(kCommandTabClosed, sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateWindowClosed(
+    const SessionID::id_type window_id) {
+  ClosedPayload payload;
+  // See comment in CreateTabClosedCommand as to why we do this.
+  memset(&payload, 0, sizeof(payload));
+  payload.id = window_id;
+  payload.close_time = base::Time::Now().ToInternalValue();
+  SessionCommand* command =
+      new SessionCommand(kCommandWindowClosed, sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateSetSelectedNavigationIndex(
+    const SessionID& tab_id,
+    int index) {
+  SelectedNavigationIndexPayload payload = { 0 };
+  payload.id = tab_id.id();
+  payload.index = index;
+  SessionCommand* command = new SessionCommand(
+      kCommandSetSelectedNavigationIndex, sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateSetWindowType(
+    const SessionID& window_id,
+    SessionWindow::WindowType type) {
+  WindowTypePayload payload = { 0 };
+  payload.id = window_id.id();
+  payload.index = static_cast<int32>(type);
+  SessionCommand* command = new SessionCommand(
+      kCommandSetWindowType, sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreatePinnedState(
+    const SessionID& tab_id,
+    bool is_pinned) {
+  PinnedStatePayload payload = { 0 };
+  payload.tab_id = tab_id.id();
+  payload.pinned_state = is_pinned;
+  SessionCommand* command =
+      new SessionCommand(kCommandSetPinnedState, sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateSessionStorageAssociated(
+    const SessionID& tab_id,
+    const std::string& session_storage_persistent_id) {
+  Pickle pickle;
+  pickle.WriteInt(tab_id.id());
+  pickle.WriteString(session_storage_persistent_id);
+  return new SessionCommand(kCommandSessionStorageAssociated, pickle);
+}
+
+SessionCommand* SessionServiceCommands::CreateSetActiveWindow(
+    const SessionID& window_id) {
+  ActiveWindowPayload payload = 0;
+  payload = window_id.id();
+  SessionCommand* command =
+      new SessionCommand(kCommandSetActiveWindow, sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateTabNavigationPathPrunedFromBack(
+    const SessionID& tab_id,
+    int count) {
+  TabNavigationPathPrunedFromBackPayload payload = { 0 };
+  payload.id = tab_id.id();
+  payload.index = count;
+  SessionCommand* command =
+      new SessionCommand(kCommandTabNavigationPathPrunedFromBack,
+                         sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateTabNavigationPathPrunedFromFront(
+    const SessionID& tab_id,
+    int count) {
+  TabNavigationPathPrunedFromFrontPayload payload = { 0 };
+  payload.id = tab_id.id();
+  payload.index = count;
+  SessionCommand* command =
+      new SessionCommand(kCommandTabNavigationPathPrunedFromFront,
+                         sizeof(payload));
+  memcpy(command->contents(), &payload, sizeof(payload));
+  return command;
+}
+
+SessionCommand* SessionServiceCommands::CreateUpdateTabNavigation(
+    const SessionID& tab_id,
+    const sessions::SerializedNavigationEntry& navigation) {
+  // TODO(skuhne): Check why this command needs to be called from the base.
+  // thus: could eliminate the use of that class here.
+  return CreateUpdateTabNavigationCommand(
+      kCommandUpdateTabNavigation,
+      tab_id.id(),
+      navigation);
+}
+
+SessionCommand* SessionServiceCommands::CreateSetTabExtensionAppID(
+    const SessionID& tab_id,
+    const std::string& extension_id) {
+  return CreateSetTabExtensionAppIDCommand(
+      kCommandSetExtensionAppID,
+      tab_id.id(),
+      extension_id);
+}
+
+SessionCommand* SessionServiceCommands::CreateSetTabUserAgentOverride(
+    const SessionID& tab_id,
+    const std::string& user_agent_override) {
+  return CreateSetTabUserAgentOverrideCommand(
+      kCommandSetTabUserAgentOverride,
+      tab_id.id(),
+      user_agent_override);
+}
+
+SessionCommand* SessionServiceCommands::CreateSetWindowAppName(
+    const SessionID& window_id,
+    const std::string& app_name) {
+  return CreateSetWindowAppNameCommand(
+      kCommandSetWindowAppName,
+      window_id.id(),
+      app_name);
+}
+
+void SessionServiceCommands::ScheduleCommand(SessionCommand* command) {
+  DCHECK(command);
+  if (ReplacePendingCommand(command))
+    return;
+  BaseSessionService::ScheduleCommand(command);
+  // Don't schedule a reset on tab closed/window closed. Otherwise we may
+  // lose tabs/windows we want to restore from if we exit right after this.
+  if (commands_since_reset() >= kWritesPerReset &&
+      (command->id() != kCommandTabClosed &&
+       command->id() != kCommandWindowClosed)) {
+    ScheduleResetCommands();
+  }
+}
+
+void SessionServiceCommands::OnGotSessionServiceCommands(
+    const SessionCallback& callback,
+    ScopedVector<SessionCommand> commands) {
+  ScopedVector<SessionWindow> valid_windows;
+  SessionID::id_type active_window_id = 0;
+
+  RestoreSessionFromCommands(
+      commands.get(), &valid_windows.get(), &active_window_id);
+  callback.Run(valid_windows.Pass(), active_window_id);
+}
+
+void SessionServiceCommands::RestoreSessionFromCommands(
+    const std::vector<SessionCommand*>& commands,
+    std::vector<SessionWindow*>* valid_windows,
+    SessionID::id_type* active_window_id) {
+  std::map<int, SessionTab*> tabs;
+  std::map<int, SessionWindow*> windows;
+
+  VLOG(1) << "RestoreSessionFromCommands " << commands.size();
+  if (CreateTabsAndWindows(commands, &tabs, &windows, active_window_id)) {
+    AddTabsToWindows(&tabs, &windows);
+    SortTabsBasedOnVisualOrderAndPrune(&windows, valid_windows);
+    UpdateSelectedTabIndex(valid_windows);
+  }
+  STLDeleteValues(&tabs);
+  // Don't delete contents of windows, that is done by the caller as all
+  // valid windows are added to valid_windows.
+}
+
+void SessionServiceCommands::UpdateSelectedTabIndex(
+    std::vector<SessionWindow*>* windows) {
+  for (std::vector<SessionWindow*>::const_iterator i = windows->begin();
+       i != windows->end(); ++i) {
+    // See note in SessionWindow as to why we do this.
+    int new_index = 0;
+    for (std::vector<SessionTab*>::const_iterator j = (*i)->tabs.begin();
+         j != (*i)->tabs.end(); ++j) {
+      if ((*j)->tab_visual_index == (*i)->selected_tab_index) {
+        new_index = static_cast<int>(j - (*i)->tabs.begin());
+        break;
+      }
+    }
+    (*i)->selected_tab_index = new_index;
+  }
+}
+
+SessionWindow* SessionServiceCommands::GetWindow(SessionID::id_type window_id,
+                                          IdToSessionWindow* windows) {
+  std::map<int, SessionWindow*>::iterator i = windows->find(window_id);
+  if (i == windows->end()) {
+    SessionWindow* window = new SessionWindow();
+    window->window_id.set_id(window_id);
+    (*windows)[window_id] = window;
+    return window;
+  }
+  return i->second;
+}
+
+SessionTab* SessionServiceCommands::GetTab(SessionID::id_type tab_id,
+                                    IdToSessionTab* tabs) {
+  DCHECK(tabs);
+  std::map<int, SessionTab*>::iterator i = tabs->find(tab_id);
+  if (i == tabs->end()) {
+    SessionTab* tab = new SessionTab();
+    tab->tab_id.set_id(tab_id);
+    (*tabs)[tab_id] = tab;
+    return tab;
+  }
+  return i->second;
+}
+
+std::vector<sessions::SerializedNavigationEntry>::iterator
+  SessionServiceCommands::FindClosestNavigationWithIndex(
+    std::vector<sessions::SerializedNavigationEntry>* navigations,
+    int index) {
+  DCHECK(navigations);
+  for (std::vector<sessions::SerializedNavigationEntry>::iterator
+           i = navigations->begin(); i != navigations->end(); ++i) {
+    if (i->index() >= index)
+      return i;
+  }
+  return navigations->end();
+}
+
+// Function used in sorting windows. Sorting is done based on window id. As
+// window ids increment for each new window, this effectively sorts by creation
+// time.
+static bool WindowOrderSortFunction(const SessionWindow* w1,
+                                    const SessionWindow* w2) {
+  return w1->window_id.id() < w2->window_id.id();
+}
+
+// Compares the two tabs based on visual index.
+static bool TabVisualIndexSortFunction(const SessionTab* t1,
+                                       const SessionTab* t2) {
+  const int delta = t1->tab_visual_index - t2->tab_visual_index;
+  return delta == 0 ? (t1->tab_id.id() < t2->tab_id.id()) : (delta < 0);
+}
+
+void SessionServiceCommands::SortTabsBasedOnVisualOrderAndPrune(
+    std::map<int, SessionWindow*>* windows,
+    std::vector<SessionWindow*>* valid_windows) {
+  std::map<int, SessionWindow*>::iterator i = windows->begin();
+  while (i != windows->end()) {
+    SessionWindow* window = i->second;
+    AppType app_type = window->app_name.empty() ? TYPE_NORMAL : TYPE_APP;
+    if (window->tabs.empty() || window->is_constrained ||
+        !ShouldTrackChangesOfWindowType(window->type, app_type)) {
+      delete window;
+      windows->erase(i++);
+    } else {
+      // Valid window; sort the tabs and add it to the list of valid windows.
+      std::sort(window->tabs.begin(), window->tabs.end(),
+                &TabVisualIndexSortFunction);
+      // Otherwise, add the window such that older windows appear first.
+      if (valid_windows->empty()) {
+        valid_windows->push_back(window);
+      } else {
+        valid_windows->insert(
+            std::upper_bound(valid_windows->begin(), valid_windows->end(),
+                             window, &WindowOrderSortFunction),
+            window);
+      }
+      ++i;
+    }
+  }
+}
+
+void SessionServiceCommands::AddTabsToWindows(std::map<int, SessionTab*>* tabs,
+                                       std::map<int, SessionWindow*>* windows) {
+  VLOG(1) << "AddTabsToWindws";
+  VLOG(1) << "Tabs " << tabs->size() << ", windows " << windows->size();
+  std::map<int, SessionTab*>::iterator i = tabs->begin();
+  while (i != tabs->end()) {
+    SessionTab* tab = i->second;
+    if (tab->window_id.id() && !tab->navigations.empty()) {
+      SessionWindow* window = GetWindow(tab->window_id.id(), windows);
+      window->tabs.push_back(tab);
+      tabs->erase(i++);
+
+      // See note in SessionTab as to why we do this.
+      std::vector<sessions::SerializedNavigationEntry>::iterator j =
+          FindClosestNavigationWithIndex(&(tab->navigations),
+                                         tab->current_navigation_index);
+      if (j == tab->navigations.end()) {
+        tab->current_navigation_index =
+            static_cast<int>(tab->navigations.size() - 1);
+      } else {
+        tab->current_navigation_index =
+            static_cast<int>(j - tab->navigations.begin());
+      }
+    } else {
+      // Never got a set tab index in window, or tabs are empty, nothing
+      // to do.
+      ++i;
+    }
+  }
+}
+
+bool SessionServiceCommands::CreateTabsAndWindows(
+    const std::vector<SessionCommand*>& data,
+    std::map<int, SessionTab*>* tabs,
+    std::map<int, SessionWindow*>* windows,
+    SessionID::id_type* active_window_id) {
+  // If the file is corrupt (command with wrong size, or unknown command), we
+  // still return true and attempt to restore what we we can.
+  VLOG(1) << "CreateTabsAndWindows";
+
+  startup_metric_utils::ScopedSlowStartupUMA
+      scoped_timer("Startup.SlowStartupSessionServiceCreateTabsAndWindows");
+
+  for (std::vector<SessionCommand*>::const_iterator i = data.begin();
+       i != data.end(); ++i) {
+    const SessionCommand::id_type kCommandSetWindowBounds2 = 10;
+    const SessionCommand* command = *i;
+
+    VLOG(1) << "Read command " << (int) command->id();
+    switch (command->id()) {
+      case kCommandSetTabWindow: {
+        SessionID::id_type payload[2];
+        if (!command->GetPayload(payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        GetTab(payload[1], tabs)->window_id.set_id(payload[0]);
+        break;
+      }
+
+      // This is here for forward migration only.  New data is saved with
+      // |kCommandSetWindowBounds3|.
+      case kCommandSetWindowBounds2: {
+        WindowBoundsPayload2 payload;
+        if (!command->GetPayload(&payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        GetWindow(payload.window_id, windows)->bounds.SetRect(payload.x,
+                                                              payload.y,
+                                                              payload.w,
+                                                              payload.h);
+        GetWindow(payload.window_id, windows)->show_state =
+            payload.is_maximized ?
+                ui::SHOW_STATE_MAXIMIZED : ui::SHOW_STATE_NORMAL;
+        break;
+      }
+
+      case kCommandSetWindowBounds3: {
+        WindowBoundsPayload3 payload;
+        if (!command->GetPayload(&payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        GetWindow(payload.window_id, windows)->bounds.SetRect(payload.x,
+                                                              payload.y,
+                                                              payload.w,
+                                                              payload.h);
+        GetWindow(payload.window_id, windows)->show_state =
+            PersistedShowStateToShowState(payload.show_state);
+        break;
+      }
+
+      case kCommandSetTabIndexInWindow: {
+        TabIndexInWindowPayload payload;
+        if (!command->GetPayload(&payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        GetTab(payload.id, tabs)->tab_visual_index = payload.index;
+        break;
+      }
+
+      case kCommandTabClosed:
+      case kCommandWindowClosed: {
+        ClosedPayload payload;
+        if (!command->GetPayload(&payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        if (command->id() == kCommandTabClosed) {
+          delete GetTab(payload.id, tabs);
+          tabs->erase(payload.id);
+        } else {
+          delete GetWindow(payload.id, windows);
+          windows->erase(payload.id);
+        }
+        break;
+      }
+
+      case kCommandTabNavigationPathPrunedFromBack: {
+        TabNavigationPathPrunedFromBackPayload payload;
+        if (!command->GetPayload(&payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        SessionTab* tab = GetTab(payload.id, tabs);
+        tab->navigations.erase(
+            FindClosestNavigationWithIndex(&(tab->navigations), payload.index),
+            tab->navigations.end());
+        break;
+      }
+
+      case kCommandTabNavigationPathPrunedFromFront: {
+        TabNavigationPathPrunedFromFrontPayload payload;
+        if (!command->GetPayload(&payload, sizeof(payload)) ||
+            payload.index <= 0) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        SessionTab* tab = GetTab(payload.id, tabs);
+
+        // Update the selected navigation index.
+        tab->current_navigation_index =
+            std::max(-1, tab->current_navigation_index - payload.index);
+
+        // And update the index of existing navigations.
+        for (std::vector<sessions::SerializedNavigationEntry>::iterator
+                 i = tab->navigations.begin();
+             i != tab->navigations.end();) {
+          i->set_index(i->index() - payload.index);
+          if (i->index() < 0)
+            i = tab->navigations.erase(i);
+          else
+            ++i;
+        }
+        break;
+      }
+
+      case kCommandUpdateTabNavigation: {
+        sessions::SerializedNavigationEntry navigation;
+        SessionID::id_type tab_id;
+        if (!RestoreUpdateTabNavigationCommand(
+            *command, &navigation, &tab_id)) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        SessionTab* tab = GetTab(tab_id, tabs);
+        std::vector<sessions::SerializedNavigationEntry>::iterator i =
+            FindClosestNavigationWithIndex(&(tab->navigations),
+                                           navigation.index());
+        if (i != tab->navigations.end() && i->index() == navigation.index())
+          *i = navigation;
+        else
+          tab->navigations.insert(i, navigation);
+        break;
+      }
+
+      case kCommandSetSelectedNavigationIndex: {
+        SelectedNavigationIndexPayload payload;
+        if (!command->GetPayload(&payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        GetTab(payload.id, tabs)->current_navigation_index = payload.index;
+        break;
+      }
+
+      case kCommandSetSelectedTabInIndex: {
+        SelectedTabInIndexPayload payload;
+        if (!command->GetPayload(&payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        GetWindow(payload.id, windows)->selected_tab_index = payload.index;
+        break;
+      }
+
+      case kCommandSetWindowType: {
+        WindowTypePayload payload;
+        if (!command->GetPayload(&payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        GetWindow(payload.id, windows)->is_constrained = false;
+        GetWindow(payload.id, windows)->type =
+            static_cast<SessionWindow::WindowType>(payload.index);
+        break;
+      }
+
+      case kCommandSetPinnedState: {
+        PinnedStatePayload payload;
+        if (!command->GetPayload(&payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        GetTab(payload.tab_id, tabs)->pinned = payload.pinned_state;
+        break;
+      }
+
+      case kCommandSetWindowAppName: {
+        SessionID::id_type window_id;
+        std::string app_name;
+        if (!RestoreSetWindowAppNameCommand(*command, &window_id, &app_name))
+          return true;
+
+        GetWindow(window_id, windows)->app_name.swap(app_name);
+        break;
+      }
+
+      case kCommandSetExtensionAppID: {
+        SessionID::id_type tab_id;
+        std::string extension_app_id;
+        if (!RestoreSetTabExtensionAppIDCommand(
+                *command, &tab_id, &extension_app_id)) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+
+        GetTab(tab_id, tabs)->extension_app_id.swap(extension_app_id);
+        break;
+      }
+
+      case kCommandSetTabUserAgentOverride: {
+        SessionID::id_type tab_id;
+        std::string user_agent_override;
+        if (!RestoreSetTabUserAgentOverrideCommand(
+                *command, &tab_id, &user_agent_override)) {
+          return true;
+        }
+
+        GetTab(tab_id, tabs)->user_agent_override.swap(user_agent_override);
+        break;
+      }
+
+      case kCommandSessionStorageAssociated: {
+        scoped_ptr<Pickle> command_pickle(command->PayloadAsPickle());
+        SessionID::id_type command_tab_id;
+        std::string session_storage_persistent_id;
+        PickleIterator iter(*command_pickle.get());
+        if (!command_pickle->ReadInt(&iter, &command_tab_id) ||
+            !command_pickle->ReadString(&iter, &session_storage_persistent_id))
+          return true;
+        // Associate the session storage back.
+        GetTab(command_tab_id, tabs)->session_storage_persistent_id =
+            session_storage_persistent_id;
+        break;
+      }
+
+      case kCommandSetActiveWindow: {
+        ActiveWindowPayload payload;
+        if (!command->GetPayload(&payload, sizeof(payload))) {
+          VLOG(1) << "Failed reading command " << command->id();
+          return true;
+        }
+        *active_window_id = payload;
+        break;
+      }
+
+      default:
+        // TODO(skuhne): This might call back into a callback handler to extend
+        // the command set for specific implementations.
+        VLOG(1) << "Failed reading an unknown command " << command->id();
+        return true;
+    }
+  }
+  return true;
+}
+
+bool SessionServiceCommands::ReplacePendingCommand(SessionCommand* command) {
+  // We optimize page navigations, which can happen quite frequently and
+  // are expensive. And activation is like Highlander, there can only be one!
+  if (command->id() != kCommandUpdateTabNavigation &&
+      command->id() != kCommandSetActiveWindow) {
+    return false;
+  }
+  for (std::vector<SessionCommand*>::reverse_iterator i =
+       pending_commands().rbegin(); i != pending_commands().rend(); ++i) {
+    SessionCommand* existing_command = *i;
+    if (command->id() == kCommandUpdateTabNavigation &&
+        existing_command->id() == kCommandUpdateTabNavigation) {
+      scoped_ptr<Pickle> command_pickle(command->PayloadAsPickle());
+      PickleIterator iterator(*command_pickle);
+      SessionID::id_type command_tab_id;
+      int command_nav_index;
+      if (!command_pickle->ReadInt(&iterator, &command_tab_id) ||
+          !command_pickle->ReadInt(&iterator, &command_nav_index)) {
+        return false;
+      }
+      SessionID::id_type existing_tab_id;
+      int existing_nav_index;
+      {
+        // Creating a pickle like this means the Pickle references the data from
+        // the command. Make sure we delete the pickle before the command, else
+        // the pickle references deleted memory.
+        scoped_ptr<Pickle> existing_pickle(existing_command->PayloadAsPickle());
+        iterator = PickleIterator(*existing_pickle);
+        if (!existing_pickle->ReadInt(&iterator, &existing_tab_id) ||
+            !existing_pickle->ReadInt(&iterator, &existing_nav_index)) {
+          return false;
+        }
+      }
+      if (existing_tab_id == command_tab_id &&
+          existing_nav_index == command_nav_index) {
+        // existing_command is an update for the same tab/index pair. Replace
+        // it with the new one. We need to add to the end of the list just in
+        // case there is a prune command after the update command.
+        delete existing_command;
+        pending_commands().erase(i.base() - 1);
+        pending_commands().push_back(command);
+        return true;
+      }
+      return false;
+    }
+    if (command->id() == kCommandSetActiveWindow &&
+        existing_command->id() == kCommandSetActiveWindow) {
+      *i = command;
+      delete existing_command;
+      return true;
+    }
+  }
+  return false;
+}