Rewrite component update service in terms of components/update_client.

The goal of this change is to re-implement the component updater by
reusing the common code in components/update_client while keeping
the its public interface the same as before, in order to minimize
changes in its existing clients.

BUG=450337

Review URL: https://codereview.chromium.org/1133443002

Cr-Commit-Position: refs/heads/master@{#331412}

1 files changed, 207 insertions, 902 deletions

diff --git a/components/component_updater/component_updater_service.cc b/components/component_updater/component_updater_service.cc
index ed49787..29b120e 100644
--- a/components/component_updater/component_updater_service.cc
+++ b/components/component_updater/component_updater_service.cc
@@ -5,10 +5,11 @@
 #include "components/component_updater/component_updater_service.h"
 
 #include <algorithm>
-#include <set>
+#include <map>
+#include <string>
+#include <utility>
 #include <vector>
 
-#include "base/at_exit.h"
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
@@ -18,1035 +19,339 @@
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/message_loop/message_loop_proxy.h"
-#include "base/observer_list.h"
 #include "base/sequenced_task_runner.h"
-#include "base/stl_util.h"
+#include "base/single_thread_task_runner.h"
+#include "base/thread_task_runner_handle.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/thread_checker.h"
 #include "base/timer/timer.h"
-#include "components/update_client/component_patcher_operation.h"
-#include "components/update_client/component_unpacker.h"
+#include "components/component_updater/component_updater_service_internal.h"
+#include "components/component_updater/timer.h"
 #include "components/update_client/configurator.h"
-#include "components/update_client/crx_downloader.h"
 #include "components/update_client/crx_update_item.h"
-#include "components/update_client/ping_manager.h"
-#include "components/update_client/update_checker.h"
 #include "components/update_client/update_client.h"
-#include "components/update_client/update_response.h"
 #include "components/update_client/utils.h"
 #include "url/gurl.h"
 
-using update_client::CrxInstaller;
-using update_client::ComponentUnpacker;
-using update_client::Configurator;
-using update_client::CrxComponent;
-using update_client::CrxDownloader;
-using update_client::CrxUpdateItem;
-using update_client::PingManager;
-using update_client::UpdateChecker;
-using update_client::UpdateResponse;
+using CrxInstaller = update_client::CrxInstaller;
+using UpdateClient = update_client::UpdateClient;
 
 namespace component_updater {
 
-// The component updater is designed to live until process shutdown, so
-// base::Bind() calls are not refcounted.
-
-namespace {
-
-// Returns true if the |proposed| version is newer than |current| version.
-bool IsVersionNewer(const Version& current, const std::string& proposed) {
-  Version proposed_ver(proposed);
-  return proposed_ver.IsValid() && current.CompareTo(proposed_ver) < 0;
-}
-
-// Returns true if a differential update is available, it has not failed yet,
-// and the configuration allows it.
-bool CanTryDiffUpdate(const CrxUpdateItem* update_item,
-                      const Configurator& config) {
-  return HasDiffUpdate(update_item) && !update_item->diff_update_failed &&
-         config.DeltasEnabled();
-}
-
-void AppendDownloadMetrics(
-    const std::vector<CrxDownloader::DownloadMetrics>& source,
-    std::vector<CrxDownloader::DownloadMetrics>* destination) {
-  destination->insert(destination->end(), source.begin(), source.end());
+CrxUpdateService::CrxUpdateService(
+    const scoped_refptr<Configurator>& config,
+    const scoped_refptr<UpdateClient>& update_client)
+    : config_(config),
+      update_client_(update_client),
+      blocking_task_runner_(config->GetSequencedTaskRunner()) {
+  AddObserver(this);
 }
 
-}  // namespace
-
-//////////////////////////////////////////////////////////////////////////////
-// The one and only implementation of the ComponentUpdateService interface. In
-// charge of running the show. The main method is ProcessPendingItems() which
-// is called periodically to do the upgrades/installs or the update checks.
-// An important consideration here is to be as "low impact" as we can to the
-// rest of the browser, so even if we have many components registered and
-// eligible for update, we only do one thing at a time with pauses in between
-// the tasks. Also when we do network requests there is only one |url_fetcher_|
-// in flight at a time.
-// There are no locks in this code, the main structure |work_items_| is mutated
-// only from the main thread. The unpack and installation is done in a blocking
-// pool thread. The network requests are done in the IO thread or in the file
-// thread.
-class CrxUpdateService : public ComponentUpdateService, public OnDemandUpdater {
- public:
-  explicit CrxUpdateService(const scoped_refptr<Configurator>& config);
-  ~CrxUpdateService() override;
-
-  // Overrides for ComponentUpdateService.
-  void AddObserver(Observer* observer) override;
-  void RemoveObserver(Observer* observer) override;
-  Status Start() override;
-  Status Stop() override;
-  Status RegisterComponent(const CrxComponent& component) override;
-  Status UnregisterComponent(const std::string& crx_id) override;
-  std::vector<std::string> GetComponentIDs() const override;
-  OnDemandUpdater& GetOnDemandUpdater() override;
-  void MaybeThrottle(const std::string& crx_id,
-                     const base::Closure& callback) override;
-  scoped_refptr<base::SequencedTaskRunner> GetSequencedTaskRunner() override;
-
-  // Context for a crx download url request.
-  struct CRXContext {
-    scoped_refptr<CrxInstaller> installer;
-    std::vector<uint8_t> pk_hash;
-    std::string id;
-    std::string fingerprint;
-    CRXContext() : installer(NULL) {}
-  };
-
- private:
-  enum ErrorCategory {
-    kErrorNone = 0,
-    kNetworkError,
-    kUnpackError,
-    kInstallError,
-  };
-
-  enum StepDelayInterval {
-    kStepDelayShort = 0,
-    kStepDelayMedium,
-    kStepDelayLong,
-  };
-
-  // Overrides for ComponentUpdateService.
-  bool GetComponentDetails(const std::string& component_id,
-                           CrxUpdateItem* item) const override;
-
-  // Overrides for OnDemandUpdater.
-  Status OnDemandUpdate(const std::string& component_id) override;
-
-  void UpdateCheckComplete(const GURL& original_url,
-                           int error,
-                           const std::string& error_message,
-                           const UpdateResponse::Results& results);
-  void OnUpdateCheckSucceeded(const UpdateResponse::Results& results);
-  void OnUpdateCheckFailed(int error, const std::string& error_message);
-
-  void DownloadProgress(const std::string& component_id,
-                        const CrxDownloader::Result& download_result);
-
-  void DownloadComplete(scoped_ptr<CRXContext> crx_context,
-                        const CrxDownloader::Result& download_result);
-
-  Status OnDemandUpdateInternal(CrxUpdateItem* item);
-  Status OnDemandUpdateWithCooldown(CrxUpdateItem* item);
-
-  void ProcessPendingItems();
-
-  // Uninstall and remove all unregistered work items.
-  void UninstallUnregisteredItems();
-
-  // Find a component that is ready to update.
-  CrxUpdateItem* FindReadyComponent() const;
-
-  // Prepares the components for an update check and initiates the request.
-  // Returns true if an update check request has been made. Returns false if
-  // no update check was needed or an error occured.
-  bool CheckForUpdates();
-
-  void UpdateComponent(CrxUpdateItem* workitem);
-
-  void ScheduleNextRun(StepDelayInterval step_delay);
-
-  void ParseResponse(const std::string& xml);
-
-  void Install(scoped_ptr<CRXContext> context, const base::FilePath& crx_path);
-
-  void EndUnpacking(const std::string& component_id,
-                    const base::FilePath& crx_path,
-                    ComponentUnpacker::Error error,
-                    int extended_error);
-
-  void DoneInstalling(const std::string& component_id,
-                      ComponentUnpacker::Error error,
-                      int extended_error);
-
-  void ChangeItemState(CrxUpdateItem* item, CrxUpdateItem::State to);
-
-  size_t ChangeItemStatus(CrxUpdateItem::State from, CrxUpdateItem::State to);
-
-  CrxUpdateItem* FindUpdateItemById(const std::string& id) const;
-
-  void NotifyObservers(Observer::Events event, const std::string& id);
-
-  bool HasOnDemandItems() const;
-
-  Status GetServiceStatus(const CrxUpdateItem::State state);
-
-  scoped_refptr<Configurator> config_;
-
-  scoped_ptr<UpdateChecker> update_checker_;
-
-  scoped_ptr<PingManager> ping_manager_;
-
-  scoped_refptr<ComponentUnpacker> unpacker_;
-
-  scoped_ptr<CrxDownloader> crx_downloader_;
-
-  // A collection of every work item.
-  typedef std::vector<CrxUpdateItem*> UpdateItems;
-  UpdateItems work_items_;
-
-  base::OneShotTimer<CrxUpdateService> timer_;
-
-  base::ThreadChecker thread_checker_;
-
-  // Used to post responses back to the main thread.
-  scoped_refptr<base::SingleThreadTaskRunner> main_task_runner_;
-
-  scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_;
-
-  bool running_;
-
-  ObserverList<Observer> observer_list_;
-
-  DISALLOW_COPY_AND_ASSIGN(CrxUpdateService);
-};
+CrxUpdateService::~CrxUpdateService() {
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-//////////////////////////////////////////////////////////////////////////////
+  for (const auto item : ready_callbacks_) {
+    item.second.Run();
+  }
 
-CrxUpdateService::CrxUpdateService(const scoped_refptr<Configurator>& config)
-    : config_(config),
-      ping_manager_(new PingManager(*config)),
-      main_task_runner_(base::MessageLoopProxy::current()),
-      blocking_task_runner_(config->GetSequencedTaskRunner()),
-      running_(false) {
-}
+  RemoveObserver(this);
 
-CrxUpdateService::~CrxUpdateService() {
-  // Because we are a singleton, at this point only the main thread should be
-  // alive, this simplifies the management of the work that could be in
-  // flight in other threads.
   Stop();
-  STLDeleteElements(&work_items_);
 }
 
 void CrxUpdateService::AddObserver(Observer* observer) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  observer_list_.AddObserver(observer);
+  update_client_->AddObserver(observer);
 }
 
 void CrxUpdateService::RemoveObserver(Observer* observer) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  observer_list_.RemoveObserver(observer);
+  update_client_->RemoveObserver(observer);
 }
 
-ComponentUpdateService::Status CrxUpdateService::Start() {
-  // Note that RegisterComponent will call Start() when the first
-  // component is registered, so it can be called twice. This way
-  // we avoid scheduling the timer if there is no work to do.
-  VLOG(1) << "CrxUpdateService starting up";
-  running_ = true;
-  if (work_items_.empty())
-    return Status::kOk;
-
-  NotifyObservers(Observer::Events::COMPONENT_UPDATER_STARTED, "");
-
-  VLOG(1) << "First update attempt will take place in "
-          << config_->InitialDelay() << " seconds";
-  timer_.Start(FROM_HERE,
-               base::TimeDelta::FromSeconds(config_->InitialDelay()),
-               this,
-               &CrxUpdateService::ProcessPendingItems);
-  return Status::kOk;
+void CrxUpdateService::Start() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  VLOG(1) << "CrxUpdateService starting up. "
+          << "First update attempt will take place in "
+          << config_->InitialDelay() << " seconds. "
+          << "Next update attempt will take place in "
+          << config_->NextCheckDelay() << " seconds. ";
+
+  timer_.Start(
+      base::TimeDelta::FromSeconds(config_->InitialDelay()),
+      base::TimeDelta::FromSeconds(config_->NextCheckDelay()),
+      base::Bind(base::IgnoreResult(&CrxUpdateService::CheckForUpdates),
+                 base::Unretained(this)));
 }
 
-// Stop the main check + update loop. In flight operations will be
-// completed.
-ComponentUpdateService::Status CrxUpdateService::Stop() {
+// Stops the update loop. In flight operations will be completed.
+void CrxUpdateService::Stop() {
+  DCHECK(thread_checker_.CalledOnValidThread());
   VLOG(1) << "CrxUpdateService stopping";
-  running_ = false;
   timer_.Stop();
-  return Status::kOk;
-}
-
-bool CrxUpdateService::HasOnDemandItems() const {
-  class Helper {
-   public:
-    static bool IsOnDemand(CrxUpdateItem* item) { return item->on_demand; }
-  };
-  return std::find_if(work_items_.begin(),
-                      work_items_.end(),
-                      Helper::IsOnDemand) != work_items_.end();
 }
 
-// This function sets the timer which will call ProcessPendingItems() or
-// ProcessRequestedItem() if there is an on_demand item.  There
-// are three kinds of waits:
-//  - a short delay, when there is immediate work to be done.
-//  - a medium delay, when there are updates to be applied within the current
-//    update cycle, or there are components that are still unchecked.
-//  - a long delay when a full check/update cycle has completed for all
-//    components.
-void CrxUpdateService::ScheduleNextRun(StepDelayInterval step_delay) {
+// Adds a component to be checked for upgrades. If the component exists it
+// it will be replaced.
+bool CrxUpdateService::RegisterComponent(const CrxComponent& component) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK(!update_checker_);
-  CHECK(!timer_.IsRunning());
-  // It could be the case that Stop() had been called while a url request
-  // or unpacking was in flight, if so we arrive here but |running_| is
-  // false. In that case do not loop again.
-  if (!running_)
-    return;
+  if (component.pk_hash.empty() || !component.version.IsValid() ||
+      !component.installer) {
+    return false;
+  }
 
-  // Keep the delay short if in the middle of an update (step_delay),
-  // or there are new requested_work_items_ that have not been processed yet.
-  int64_t delay_seconds = 0;
-  if (!HasOnDemandItems()) {
-    switch (step_delay) {
-      case kStepDelayShort:
-        delay_seconds = config_->StepDelay();
-        break;
-      case kStepDelayMedium:
-        delay_seconds = config_->StepDelayMedium();
-        break;
-      case kStepDelayLong:
-        delay_seconds = config_->NextCheckDelay();
-        break;
-    }
-  } else {
-    delay_seconds = config_->StepDelay();
+  // Update the registration data if the component has been registered before.
+  const std::string id(GetCrxComponentID(component));
+  auto it = components_.find(id);
+  if (it != components_.end()) {
+    it->second = component;
+    return true;
   }
 
-  if (step_delay != kStepDelayShort) {
-    NotifyObservers(Observer::Events::COMPONENT_UPDATER_SLEEPING, "");
+  components_.insert(std::make_pair(id, component));
+  components_order_.push_back(id);
 
-    // Zero is only used for unit tests.
-    if (0 == delay_seconds)
-      return;
-  }
+  // Create an initial state for this component. The state is mutated in
+  // response to events from the UpdateClient instance.
+  CrxUpdateItem item;
+  item.id = id;
+  item.component = component;
+  const auto inserted = component_states_.insert(std::make_pair(id, item));
+  DCHECK(inserted.second);
 
-  VLOG(1) << "Scheduling next run to occur in " << delay_seconds << " seconds";
-  timer_.Start(FROM_HERE,
-               base::TimeDelta::FromSeconds(delay_seconds),
-               this,
-               &CrxUpdateService::ProcessPendingItems);
-}
+  // Start the timer if this is the first component registered. The first timer
+  // event occurs after an interval defined by the component update
+  // configurator. The subsequent timer events are repeated with a period
+  // defined by the same configurator.
+  if (components_.size() == 1)
+    Start();
 
-// Given a extension-like component id, find the associated component.
-CrxUpdateItem* CrxUpdateService::FindUpdateItemById(
-    const std::string& id) const {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  CrxUpdateItem::FindById finder(id);
-  UpdateItems::const_iterator it =
-      std::find_if(work_items_.begin(), work_items_.end(), finder);
-  return it != work_items_.end() ? *it : NULL;
+  return true;
 }
 
-// Changes a component's state, clearing on_demand and firing notifications as
-// necessary. By convention, this is the only function that can change a
-// CrxUpdateItem's |state|.
-// TODO(waffles): Do we want to add DCHECKS for valid state transitions here?
-void CrxUpdateService::ChangeItemState(CrxUpdateItem* item,
-                                       CrxUpdateItem::State to) {
+bool CrxUpdateService::UnregisterComponent(const std::string& id) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  if (to == CrxUpdateItem::State::kNoUpdate ||
-      to == CrxUpdateItem::State::kUpdated ||
-      to == CrxUpdateItem::State::kUpToDate) {
-    item->on_demand = false;
-  }
+  auto it = components_.find(id);
+  if (it == components_.end())
+    return false;
 
-  item->state = to;
-
-  switch (to) {
-    case CrxUpdateItem::State::kCanUpdate:
-      NotifyObservers(Observer::Events::COMPONENT_UPDATE_FOUND, item->id);
-      break;
-    case CrxUpdateItem::State::kUpdatingDiff:
-    case CrxUpdateItem::State::kUpdating:
-      NotifyObservers(Observer::Events::COMPONENT_UPDATE_READY, item->id);
-      break;
-    case CrxUpdateItem::State::kUpdated:
-      NotifyObservers(Observer::Events::COMPONENT_UPDATED, item->id);
-      break;
-    case CrxUpdateItem::State::kUpToDate:
-    case CrxUpdateItem::State::kNoUpdate:
-      NotifyObservers(Observer::Events::COMPONENT_NOT_UPDATED, item->id);
-      break;
-    case CrxUpdateItem::State::kNew:
-    case CrxUpdateItem::State::kChecking:
-    case CrxUpdateItem::State::kDownloading:
-    case CrxUpdateItem::State::kDownloadingDiff:
-    case CrxUpdateItem::State::kDownloaded:
-    case CrxUpdateItem::State::kLastStatus:
-      // No notification for these states.
-      break;
-  }
+  DCHECK_EQ(id, it->first);
 
-  // Free possible pending network requests.
-  if ((to == CrxUpdateItem::State::kUpdated) ||
-      (to == CrxUpdateItem::State::kUpToDate) ||
-      (to == CrxUpdateItem::State::kNoUpdate)) {
-    for (std::vector<base::Closure>::iterator it =
-             item->ready_callbacks.begin();
-         it != item->ready_callbacks.end();
-         ++it) {
-      it->Run();
-    }
-    item->ready_callbacks.clear();
+  // Delay the uninstall of the component if the component is being updated.
+  if (update_client_->IsUpdating(id)) {
+    components_pending_unregistration_.push_back(id);
+    return true;
   }
-}
 
-// Changes all the components in |work_items_| that have |from| state to
-// |to| state and returns how many have been changed.
-size_t CrxUpdateService::ChangeItemStatus(CrxUpdateItem::State from,
-                                          CrxUpdateItem::State to) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  size_t count = 0;
-  for (UpdateItems::iterator it = work_items_.begin();
-       it != work_items_.end();
-       ++it) {
-    CrxUpdateItem* item = *it;
-    if (item->state == from) {
-      ChangeItemState(item, to);
-      ++count;
-    }
-  }
-  return count;
+  return DoUnregisterComponent(it->second);
 }
 
-// Adds a component to be checked for upgrades. If the component exists it
-// it will be replaced and the return code is Status::kReplaced.
-ComponentUpdateService::Status CrxUpdateService::RegisterComponent(
-    const CrxComponent& component) {
+bool CrxUpdateService::DoUnregisterComponent(const CrxComponent& component) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  if (component.pk_hash.empty() || !component.version.IsValid() ||
-      !component.installer)
-    return Status::kError;
-
-  std::string id(GetCrxComponentID(component));
-  CrxUpdateItem* uit = FindUpdateItemById(id);
-  if (uit) {
-    uit->component = component;
-    uit->unregistered = false;
-    return Status::kReplaced;
-  }
 
-  uit = new CrxUpdateItem;
-  uit->id.swap(id);
-  uit->component = component;
-
-  work_items_.push_back(uit);
-
-  // If this is the first component registered we call Start to
-  // schedule the first timer. Otherwise, reset the timer to trigger another
-  // pass over the work items, if the component updater is sleeping, fact
-  // indicated by a running timer. If the timer is not running, it means that
-  // the service is busy updating something, and in that case, this component
-  // will be picked up at the next pass.
-  if (running_) {
-    if (work_items_.size() == 1) {
-      Start();
-    } else if (timer_.IsRunning()) {
-        timer_.Start(FROM_HERE,
-                     base::TimeDelta::FromSeconds(config_->InitialDelay()),
-                     this,
-                     &CrxUpdateService::ProcessPendingItems);
-    }
-  }
+  const auto id = GetCrxComponentID(component);
+  DCHECK(ready_callbacks_.find(id) == ready_callbacks_.end());
 
-  return Status::kOk;
-}
+  const bool result = component.installer->Uninstall();
 
-ComponentUpdateService::Status CrxUpdateService::UnregisterComponent(
-    const std::string& crx_id) {
-  auto it = std::find_if(work_items_.begin(), work_items_.end(),
-                         CrxUpdateItem::FindById(crx_id));
-  if (it == work_items_.end())
-    return Status::kError;
+  const auto pos =
+      std::find(components_order_.begin(), components_order_.end(), id);
+  if (pos != components_order_.end())
+    components_order_.erase(pos);
 
-  (*it)->unregistered = true;
+  components_.erase(id);
+  component_states_.erase(id);
 
-  ScheduleNextRun(kStepDelayShort);
-  return Status::kOk;
+  return result;
 }
 
 std::vector<std::string> CrxUpdateService::GetComponentIDs() const {
   DCHECK(thread_checker_.CalledOnValidThread());
-  std::vector<std::string> component_ids;
-  for (UpdateItems::const_iterator it = work_items_.begin();
-       it != work_items_.end();
-       ++it) {
-    const CrxUpdateItem* item = *it;
-    component_ids.push_back(item->id);
-  }
-  return component_ids;
+  std::vector<std::string> ids;
+  for (const auto& it : components_)
+    ids.push_back(it.first);
+  return ids;
 }
 
 OnDemandUpdater& CrxUpdateService::GetOnDemandUpdater() {
+  DCHECK(thread_checker_.CalledOnValidThread());
   return *this;
 }
 
-void CrxUpdateService::MaybeThrottle(const std::string& crx_id,
-                                     const base::Closure& callback) {
+const CrxComponent* CrxUpdateService::GetComponent(
+    const std::string& id) const {
   DCHECK(thread_checker_.CalledOnValidThread());
-  // Check if we can on-demand update, else unblock the request anyway.
-  CrxUpdateItem* item = FindUpdateItemById(crx_id);
-  Status status = OnDemandUpdateWithCooldown(item);
-  if (status == Status::kOk || status == Status::kInProgress) {
-    item->ready_callbacks.push_back(callback);
-    return;
-  }
-  callback.Run();
+  const auto it(components_.find(id));
+  return it != components_.end() ? &(it->second) : NULL;
 }
 
-scoped_refptr<base::SequencedTaskRunner>
-CrxUpdateService::GetSequencedTaskRunner() {
-  return blocking_task_runner_;
-}
-
-bool CrxUpdateService::GetComponentDetails(const std::string& component_id,
-                                           CrxUpdateItem* item) const {
+const CrxUpdateItem* CrxUpdateService::GetComponentState(
+    const std::string& id) const {
   DCHECK(thread_checker_.CalledOnValidThread());
-  const CrxUpdateItem* crx_update_item(FindUpdateItemById(component_id));
-  if (crx_update_item)
-    *item = *crx_update_item;
-  return crx_update_item != NULL;
+  const auto it(component_states_.find(id));
+  return it != component_states_.end() ? &it->second : NULL;
 }
 
-// Start the process of checking for an update, for a particular component
-// that was previously registered.
-// |component_id| is a value returned from GetCrxComponentID().
-ComponentUpdateService::Status CrxUpdateService::OnDemandUpdate(
-    const std::string& component_id) {
-  return OnDemandUpdateInternal(FindUpdateItemById(component_id));
-}
-
-// This is the main loop of the component updater. It updates one component
-// at a time if updates are available. Otherwise, it does an update check or
-// takes a long sleep until the loop runs again.
-void CrxUpdateService::ProcessPendingItems() {
+void CrxUpdateService::MaybeThrottle(const std::string& id,
+                                     const base::Closure& callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
-
-  CrxUpdateItem* ready_upgrade = FindReadyComponent();
-  if (ready_upgrade) {
-    UpdateComponent(ready_upgrade);
-    return;
-  }
-
-  UninstallUnregisteredItems();
-
-  if (!CheckForUpdates())
-    ScheduleNextRun(kStepDelayLong);
-}
-
-void CrxUpdateService::UninstallUnregisteredItems() {
-  std::vector<CrxUpdateItem*> new_work_items;
-  for (CrxUpdateItem* item : work_items_) {
-    scoped_ptr<CrxUpdateItem> owned_item(item);
-    if (owned_item->unregistered) {
-      const bool success = owned_item->component.installer->Uninstall();
-      DCHECK(success);
-    } else {
-      new_work_items.push_back(owned_item.release());
+  auto it = components_.find(id);
+  if (it != components_.end()) {
+    DCHECK_EQ(it->first, id);
+    if (OnDemandUpdateWithCooldown(id)) {
+      ready_callbacks_.insert(std::make_pair(id, callback));
+      return;
     }
   }
-  new_work_items.swap(work_items_);
-}
 
-CrxUpdateItem* CrxUpdateService::FindReadyComponent() const {
-  class Helper {
-   public:
-    static bool IsReadyOnDemand(CrxUpdateItem* item) {
-      return item->on_demand && IsReady(item);
-    }
-    static bool IsReady(CrxUpdateItem* item) {
-      return item->state == CrxUpdateItem::State::kCanUpdate;
-    }
-  };
-
-  std::vector<CrxUpdateItem*>::const_iterator it = std::find_if(
-      work_items_.begin(), work_items_.end(), Helper::IsReadyOnDemand);
-  if (it != work_items_.end())
-    return *it;
-  it = std::find_if(work_items_.begin(), work_items_.end(), Helper::IsReady);
-  if (it != work_items_.end())
-    return *it;
-  return NULL;
+  callback.Run();  // Unblock the request if the request can't be throttled.
 }
 
-// Prepares the components for an update check and initiates the request.
-// On demand components are always included in the update check request.
-// Otherwise, only include components that have not been checked recently.
-bool CrxUpdateService::CheckForUpdates() {
-  const base::TimeDelta minimum_recheck_wait_time =
-      base::TimeDelta::FromSeconds(config_->MinimumReCheckWait());
-  const base::Time now(base::Time::Now());
-
-  std::vector<CrxUpdateItem*> items_to_check;
-  for (size_t i = 0; i != work_items_.size(); ++i) {
-    CrxUpdateItem* item = work_items_[i];
-    DCHECK(item->state == CrxUpdateItem::State::kNew ||
-           item->state == CrxUpdateItem::State::kNoUpdate ||
-           item->state == CrxUpdateItem::State::kUpToDate ||
-           item->state == CrxUpdateItem::State::kUpdated);
-
-    const base::TimeDelta time_since_last_checked(now - item->last_check);
-
-    if (!item->on_demand &&
-        time_since_last_checked < minimum_recheck_wait_time) {
-      VLOG(1) << "Skipping check for component update: id=" << item->id
-              << ", time_since_last_checked="
-              << time_since_last_checked.InSeconds()
-              << " seconds: too soon to check for an update";
-      continue;
-    }
-
-    VLOG(1) << "Scheduling update check for component id=" << item->id
-            << ", time_since_last_checked="
-            << time_since_last_checked.InSeconds() << " seconds";
-
-    item->last_check = now;
-    item->crx_urls.clear();
-    item->crx_diffurls.clear();
-    item->previous_version = item->component.version;
-    item->next_version = Version();
-    item->previous_fp = item->component.fingerprint;
-    item->next_fp.clear();
-    item->diff_update_failed = false;
-    item->error_category = 0;
-    item->error_code = 0;
-    item->extra_code1 = 0;
-    item->diff_error_category = 0;
-    item->diff_error_code = 0;
-    item->diff_extra_code1 = 0;
-    item->download_metrics.clear();
-
-    items_to_check.push_back(item);
-
-    ChangeItemState(item, CrxUpdateItem::State::kChecking);
-  }
+bool CrxUpdateService::OnDemandUpdate(const std::string& id) {
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-  if (items_to_check.empty())
+  if (!GetComponent(id))
     return false;
 
-  update_checker_ = UpdateChecker::Create(*config_).Pass();
-  return update_checker_->CheckForUpdates(
-      items_to_check,
-      config_->ExtraRequestParams(),
-      base::Bind(&CrxUpdateService::UpdateCheckComplete,
-                 base::Unretained(this)));
+  return OnDemandUpdateInternal(id);
 }
 
-void CrxUpdateService::UpdateComponent(CrxUpdateItem* workitem) {
-  scoped_ptr<CRXContext> crx_context(new CRXContext);
-  crx_context->pk_hash = workitem->component.pk_hash;
-  crx_context->id = workitem->id;
-  crx_context->installer = workitem->component.installer;
-  crx_context->fingerprint = workitem->next_fp;
-  const std::vector<GURL>* urls = NULL;
-  bool allow_background_download = false;
-  if (CanTryDiffUpdate(workitem, *config_)) {
-    urls = &workitem->crx_diffurls;
-    ChangeItemState(workitem, CrxUpdateItem::State::kDownloadingDiff);
-  } else {
-    // Background downloads are enabled only for selected components and
-    // only for full downloads (see issue 340448).
-    allow_background_download = workitem->component.allow_background_download;
-    urls = &workitem->crx_urls;
-    ChangeItemState(workitem, CrxUpdateItem::State::kDownloading);
-  }
-
-  // On demand component updates are always downloaded in foreground.
-  const bool is_background_download = !workitem->on_demand &&
-                                      allow_background_download &&
-                                      config_->UseBackgroundDownloader();
-
-  crx_downloader_.reset(
-      CrxDownloader::Create(is_background_download, config_->RequestContext(),
-                            blocking_task_runner_,
-                            config_->GetSingleThreadTaskRunner()).release());
-  crx_downloader_->set_progress_callback(
-      base::Bind(&CrxUpdateService::DownloadProgress,
-                 base::Unretained(this),
-                 crx_context->id));
-  crx_downloader_->StartDownload(*urls,
-                                 base::Bind(&CrxUpdateService::DownloadComplete,
-                                            base::Unretained(this),
-                                            base::Passed(&crx_context)));
-}
-
-void CrxUpdateService::UpdateCheckComplete(
-    const GURL& original_url,
-    int error,
-    const std::string& error_message,
-    const UpdateResponse::Results& results) {
+bool CrxUpdateService::OnDemandUpdateWithCooldown(const std::string& id) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  VLOG(1) << "Update check completed from: " << original_url.spec();
-  update_checker_.reset();
-  if (!error)
-    OnUpdateCheckSucceeded(results);
-  else
-    OnUpdateCheckFailed(error, error_message);
-}
-
-// Handles a valid Omaha update check response by matching the results with
-// the registered components which were checked for updates.
-// If updates are found, prepare the components for the actual version upgrade.
-// One of these components will be drafted for the upgrade next time
-// ProcessPendingItems is called.
-void CrxUpdateService::OnUpdateCheckSucceeded(
-    const UpdateResponse::Results& results) {
-  size_t num_updates_pending = 0;
-  DCHECK(thread_checker_.CalledOnValidThread());
-  VLOG(1) << "Update check succeeded.";
-  std::vector<UpdateResponse::Result>::const_iterator it;
-  for (it = results.list.begin(); it != results.list.end(); ++it) {
-    CrxUpdateItem* crx = FindUpdateItemById(it->extension_id);
-    if (!crx)
-      continue;
-
-    if (crx->state != CrxUpdateItem::State::kChecking) {
-      NOTREACHED();
-      continue;  // Not updating this component now.
-    }
-
-    if (it->manifest.version.empty()) {
-      // No version means no update available.
-      ChangeItemState(crx, CrxUpdateItem::State::kNoUpdate);
-      VLOG(1) << "No update available for component: " << crx->id;
-      continue;
-    }
-
-    if (!IsVersionNewer(crx->component.version, it->manifest.version)) {
-      // The component is up to date.
-      ChangeItemState(crx, CrxUpdateItem::State::kUpToDate);
-      VLOG(1) << "Component already up-to-date: " << crx->id;
-      continue;
-    }
-
-    if (!it->manifest.browser_min_version.empty()) {
-      if (IsVersionNewer(config_->GetBrowserVersion(),
-                         it->manifest.browser_min_version)) {
-        // The component is not compatible with this Chrome version.
-        VLOG(1) << "Ignoring incompatible component: " << crx->id;
-        ChangeItemState(crx, CrxUpdateItem::State::kNoUpdate);
-        continue;
-      }
-    }
-
-    if (it->manifest.packages.size() != 1) {
-      // Assume one and only one package per component.
-      VLOG(1) << "Ignoring multiple packages for component: " << crx->id;
-      ChangeItemState(crx, CrxUpdateItem::State::kNoUpdate);
-      continue;
-    }
-
-    // Parse the members of the result and queue an upgrade for this component.
-    crx->next_version = Version(it->manifest.version);
-
-    VLOG(1) << "Update found for component: " << crx->id;
-
-    typedef UpdateResponse::Result::Manifest::Package Package;
-    const Package& package(it->manifest.packages[0]);
-    crx->next_fp = package.fingerprint;
 
-    // Resolve the urls by combining the base urls with the package names.
-    for (size_t i = 0; i != it->crx_urls.size(); ++i) {
-      const GURL url(it->crx_urls[i].Resolve(package.name));
-      if (url.is_valid())
-        crx->crx_urls.push_back(url);
-    }
-    for (size_t i = 0; i != it->crx_diffurls.size(); ++i) {
-      const GURL url(it->crx_diffurls[i].Resolve(package.namediff));
-      if (url.is_valid())
-        crx->crx_diffurls.push_back(url);
-    }
+  DCHECK(GetComponent(id));
 
-    ChangeItemState(crx, CrxUpdateItem::State::kCanUpdate);
-    ++num_updates_pending;
+  // Check if the request is too soon.
+  const auto component_state(GetComponentState(id));
+  if (component_state) {
+    base::TimeDelta delta = base::Time::Now() - component_state->last_check;
+    if (delta < base::TimeDelta::FromSeconds(config_->OnDemandDelay()))
+      return false;
   }
 
-  // All components that are not included in the update response are
-  // considered up to date.
-  ChangeItemStatus(CrxUpdateItem::State::kChecking,
-                   CrxUpdateItem::State::kUpToDate);
-
-  // If there are updates pending we do a short wait, otherwise we take
-  // a longer delay until we check the components again.
-  ScheduleNextRun(num_updates_pending > 0 ? kStepDelayShort : kStepDelayLong);
+  return OnDemandUpdateInternal(id);
 }
 
-void CrxUpdateService::OnUpdateCheckFailed(int error,
-                                           const std::string& error_message) {
+bool CrxUpdateService::OnDemandUpdateInternal(const std::string& id) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK(error);
-  size_t count = ChangeItemStatus(CrxUpdateItem::State::kChecking,
-                                  CrxUpdateItem::State::kNoUpdate);
-  DCHECK_GT(count, 0ul);
-  VLOG(1) << "Update check failed.";
-  ScheduleNextRun(kStepDelayLong);
-}
 
-// Called when progress is being made downloading a CRX. The progress may
-// not monotonically increase due to how the CRX downloader switches between
-// different downloaders and fallback urls.
-void CrxUpdateService::DownloadProgress(
-    const std::string& component_id,
-    const CrxDownloader::Result& download_result) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  NotifyObservers(Observer::Events::COMPONENT_UPDATE_DOWNLOADING, component_id);
+  update_client_->Install(
+      id, base::Bind(&CrxUpdateService::OnUpdate, base::Unretained(this)),
+      base::Bind(&CrxUpdateService::OnUpdateComplete, base::Unretained(this)));
+
+  return true;
 }
 
-// Called when the CRX package has been downloaded to a temporary location.
-// Here we fire the notifications and schedule the component-specific installer
-// to be called in the file thread.
-void CrxUpdateService::DownloadComplete(
-    scoped_ptr<CRXContext> crx_context,
-    const CrxDownloader::Result& download_result) {
+bool CrxUpdateService::CheckForUpdates() {
   DCHECK(thread_checker_.CalledOnValidThread());
-
-  CrxUpdateItem* crx = FindUpdateItemById(crx_context->id);
-
-  DCHECK(crx->state == CrxUpdateItem::State::kDownloadingDiff ||
-         crx->state == CrxUpdateItem::State::kDownloading);
-
-  AppendDownloadMetrics(crx_downloader_->download_metrics(),
-                        &crx->download_metrics);
-
-  crx_downloader_.reset();
-
-  if (download_result.error) {
-    if (crx->state == CrxUpdateItem::State::kDownloadingDiff) {
-      crx->diff_error_category = kNetworkError;
-      crx->diff_error_code = download_result.error;
-      crx->diff_update_failed = true;
-      size_t count = ChangeItemStatus(CrxUpdateItem::State::kDownloadingDiff,
-                                      CrxUpdateItem::State::kCanUpdate);
-      DCHECK_EQ(count, 1ul);
-
-      ScheduleNextRun(kStepDelayShort);
-      return;
-    }
-    crx->error_category = kNetworkError;
-    crx->error_code = download_result.error;
-    size_t count = ChangeItemStatus(CrxUpdateItem::State::kDownloading,
-                                    CrxUpdateItem::State::kNoUpdate);
-    DCHECK_EQ(count, 1ul);
-
-    // At this point, since both the differential and the full downloads failed,
-    // the update for this component has finished with an error.
-    ping_manager_->OnUpdateComplete(crx);
-
-    // Move on to the next update, if there is one available.
-    ScheduleNextRun(kStepDelayMedium);
-  } else {
-    size_t count = 0;
-    if (crx->state == CrxUpdateItem::State::kDownloadingDiff) {
-      count = ChangeItemStatus(CrxUpdateItem::State::kDownloadingDiff,
-                               CrxUpdateItem::State::kUpdatingDiff);
-    } else {
-      count = ChangeItemStatus(CrxUpdateItem::State::kDownloading,
-                               CrxUpdateItem::State::kUpdating);
-    }
-    DCHECK_EQ(count, 1ul);
-
-    // Why unretained? See comment at top of file.
-    blocking_task_runner_->PostDelayedTask(
-        FROM_HERE,
-        base::Bind(&CrxUpdateService::Install,
-                   base::Unretained(this),
-                   base::Passed(&crx_context),
-                   download_result.response),
-        base::TimeDelta::FromMilliseconds(config_->StepDelay()));
+  std::vector<std::string> ids;
+  for (const auto id : components_order_) {
+    DCHECK(components_.find(id) != components_.end());
+    ids.push_back(id);
   }
-}
 
-// Install consists of digital signature verification, unpacking and then
-// calling the component specific installer. All that is handled by the
-// |unpacker_|. If there is an error this function is in charge of deleting
-// the files created.
-void CrxUpdateService::Install(scoped_ptr<CRXContext> context,
-                               const base::FilePath& crx_path) {
-  // This function owns the file at |crx_path| and the |context| object.
-  unpacker_ = new ComponentUnpacker(context->pk_hash,
-                                    crx_path,
-                                    context->fingerprint,
-                                    context->installer,
-                                    config_->CreateOutOfProcessPatcher(),
-                                    blocking_task_runner_);
-  unpacker_->Unpack(base::Bind(&CrxUpdateService::EndUnpacking,
-                               base::Unretained(this),
-                               context->id,
-                               crx_path));
+  update_client_->Update(
+      ids, base::Bind(&CrxUpdateService::OnUpdate, base::Unretained(this)),
+      base::Bind(&CrxUpdateService::OnUpdateComplete, base::Unretained(this)));
+
+  return true;
 }
 
-void CrxUpdateService::EndUnpacking(const std::string& component_id,
-                                    const base::FilePath& crx_path,
-                                    ComponentUnpacker::Error error,
-                                    int extended_error) {
-  if (!update_client::DeleteFileAndEmptyParentDirectory(crx_path))
-    NOTREACHED() << crx_path.value();
-  main_task_runner_->PostDelayedTask(
-      FROM_HERE,
-      base::Bind(&CrxUpdateService::DoneInstalling,
-                 base::Unretained(this),
-                 component_id,
-                 error,
-                 extended_error),
-      base::TimeDelta::FromMilliseconds(config_->StepDelay()));
-  // Reset the unpacker last, otherwise we free our own arguments.
-  unpacker_ = NULL;
+scoped_refptr<base::SequencedTaskRunner>
+CrxUpdateService::GetSequencedTaskRunner() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  return blocking_task_runner_;
 }
 
-// Installation has been completed. Adjust the component state and
-// schedule the next check. Schedule a short delay before trying the full
-// update when the differential update failed.
-void CrxUpdateService::DoneInstalling(const std::string& component_id,
-                                      ComponentUnpacker::Error error,
-                                      int extra_code) {
+bool CrxUpdateService::GetComponentDetails(const std::string& id,
+                                           CrxUpdateItem* item) const {
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  ErrorCategory error_category = kErrorNone;
-  switch (error) {
-    case ComponentUnpacker::kNone:
-      break;
-    case ComponentUnpacker::kInstallerError:
-      error_category = kInstallError;
-      break;
-    default:
-      error_category = kUnpackError;
-      break;
+  // First, if this component is currently being updated, return its state from
+  // the update client.
+  if (update_client_->GetCrxUpdateState(id, item))
+    return true;
+
+  // Otherwise, return the last seen state of the component, if such a
+  // state exists.
+  const auto component_states_it = component_states_.find(id);
+  if (component_states_it != component_states_.end()) {
+    *item = component_states_it->second;
+    return true;
   }
 
-  const bool is_success = error == ComponentUnpacker::kNone;
-
-  CrxUpdateItem* item = FindUpdateItemById(component_id);
+  return false;
+}
 
-  if (item->state == CrxUpdateItem::State::kUpdatingDiff && !is_success) {
-    item->diff_error_category = error_category;
-    item->diff_error_code = error;
-    item->diff_extra_code1 = extra_code;
-    item->diff_update_failed = true;
-    size_t count = ChangeItemStatus(CrxUpdateItem::State::kUpdatingDiff,
-                                    CrxUpdateItem::State::kCanUpdate);
-    DCHECK_EQ(count, 1ul);
-    ScheduleNextRun(kStepDelayShort);
-    return;
-  }
+void CrxUpdateService::OnUpdate(const std::vector<std::string>& ids,
+                                std::vector<CrxComponent>* components) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(components->empty());
 
-  if (is_success) {
-    item->component.version = item->next_version;
-    item->component.fingerprint = item->next_fp;
-    ChangeItemState(item, CrxUpdateItem::State::kUpdated);
-  } else {
-    item->error_category = error_category;
-    item->error_code = error;
-    item->extra_code1 = extra_code;
-    ChangeItemState(item, CrxUpdateItem::State::kNoUpdate);
+  for (const auto& id : ids) {
+    const auto registered_component(GetComponent(id));
+    if (registered_component) {
+      components->push_back(*registered_component);
+    }
   }
-
-  ping_manager_->OnUpdateComplete(item);
-
-  // Move on to the next update, if there is one available.
-  ScheduleNextRun(kStepDelayMedium);
 }
 
-void CrxUpdateService::NotifyObservers(Observer::Events event,
-                                       const std::string& id) {
+void CrxUpdateService::OnUpdateComplete(int error) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  FOR_EACH_OBSERVER(Observer, observer_list_, OnEvent(event, id));
-}
+  VLOG(1) << "Update completed with error " << error;
 
-ComponentUpdateService::Status CrxUpdateService::OnDemandUpdateWithCooldown(
-    CrxUpdateItem* uit) {
-  if (!uit)
-    return Status::kError;
-
-  // Check if the request is too soon.
-  base::TimeDelta delta = base::Time::Now() - uit->last_check;
-  if (delta < base::TimeDelta::FromSeconds(config_->OnDemandDelay()))
-    return Status::kError;
-
-  return OnDemandUpdateInternal(uit);
+  for (const auto id : components_pending_unregistration_) {
+    if (!update_client_->IsUpdating(id)) {
+      const auto component = GetComponent(id);
+      if (component)
+        DoUnregisterComponent(*component);
+    }
+  }
 }
 
-ComponentUpdateService::Status CrxUpdateService::OnDemandUpdateInternal(
-    CrxUpdateItem* uit) {
-  if (!uit)
-    return Status::kError;
-
-  uit->on_demand = true;
-
-  // If there is an update available for this item, then continue processing
-  // the update. This is an artifact of how update checks are done: in addition
-  // to the on-demand item, the update check may include other items as well.
-  if (uit->state != CrxUpdateItem::State::kCanUpdate) {
-    Status service_status = GetServiceStatus(uit->state);
-    // If the item is already in the process of being updated, there is
-    // no point in this call, so return Status::kInProgress.
-    if (service_status == Status::kInProgress)
-      return service_status;
-
-    // Otherwise the item was already checked a while back (or it is new),
-    // set its state to kNew to give it a slightly higher priority.
-    ChangeItemState(uit, CrxUpdateItem::State::kNew);
-  }
+void CrxUpdateService::OnEvent(Events event, const std::string& id) {
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-  // In case the current delay is long, set the timer to a shorter value
-  // to get the ball rolling.
-  if (timer_.IsRunning()) {
-    timer_.Stop();
-    timer_.Start(FROM_HERE,
-                 base::TimeDelta::FromSeconds(config_->StepDelay()),
-                 this,
-                 &CrxUpdateService::ProcessPendingItems);
+  // Unblock all throttles for the component.
+  if (event == Observer::Events::COMPONENT_UPDATED ||
+      event == Observer::Events::COMPONENT_NOT_UPDATED) {
+    auto callbacks = ready_callbacks_.equal_range(id);
+    for (auto it = callbacks.first; it != callbacks.second; ++it) {
+      it->second.Run();
+    }
+    ready_callbacks_.erase(id);
   }
 
-  return Status::kOk;
-}
+  CrxUpdateItem update_item;
+  if (!update_client_->GetCrxUpdateState(id, &update_item))
+    return;
 
-ComponentUpdateService::Status CrxUpdateService::GetServiceStatus(
-    CrxUpdateItem::State state) {
-  switch (state) {
-    case CrxUpdateItem::State::kChecking:
-    case CrxUpdateItem::State::kCanUpdate:
-    case CrxUpdateItem::State::kDownloadingDiff:
-    case CrxUpdateItem::State::kDownloading:
-    case CrxUpdateItem::State::kDownloaded:
-    case CrxUpdateItem::State::kUpdatingDiff:
-    case CrxUpdateItem::State::kUpdating:
-      return Status::kInProgress;
-    case CrxUpdateItem::State::kNew:
-    case CrxUpdateItem::State::kUpdated:
-    case CrxUpdateItem::State::kUpToDate:
-    case CrxUpdateItem::State::kNoUpdate:
-      return Status::kOk;
-    case CrxUpdateItem::State::kLastStatus:
-      NOTREACHED() << static_cast<int>(state);
+  // Update the state of the item.
+  auto it = component_states_.find(id);
+  DCHECK(it != component_states_.end());
+  it->second = update_item;
+
+  // Update the component registration with the new version.
+  if (event == Observer::Events::COMPONENT_UPDATED) {
+    auto component(const_cast<CrxComponent*>(GetComponent(id)));
+    if (component) {
+      component->version = update_item.next_version;
+      component->fingerprint = update_item.next_fp;
+    }
   }
-  return Status::kError;
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 // The component update factory. Using the component updater as a singleton
 // is the job of the browser process.
+// TODO(sorin): consider making this a singleton.
 scoped_ptr<ComponentUpdateService> ComponentUpdateServiceFactory(
     const scoped_refptr<Configurator>& config) {
   DCHECK(config);
-  return scoped_ptr<ComponentUpdateService>(new CrxUpdateService(config));
+  auto update_client = update_client::UpdateClientFactory(config);
+  return scoped_ptr<ComponentUpdateService>(
+      new CrxUpdateService(config, update_client.Pass()));
 }
 
 }  // namespace component_updater