Make IOSChromeBrowsingDataRemover re-entrant

Refactor IOSChromeBrowsingDataRemover to have a queue of
pending removals (based on similar refactor that happened
to BrowsingDataRemover in //content).

Remove helper class BrowsingDataRemoverHelper as it is
now redundant (it implemented the pending removal tasks
queue).

Change IOSChromeBrowsingDataRemover from thread-affinity
to sequence-affinity (as is recommended).

Fix references to old enumeration RemoveDataMask.

Bug: none
Change-Id: I4d18b2d0db59954af723e72af034b57acdc7e85d
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Reviewed-on: https://chromium-review.googlesource.com/918666
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537313}

ios/chrome/browser/browsing_data/BUILD.gn

@@ -11,8 +11,6 @@ source_set("browsing_data_remove_mask") {
 
 source_set("browsing_data") {
   sources = [
-    "browsing_data_remover_helper.cc",
-    "browsing_data_remover_helper.h",
     "ios_chrome_browsing_data_remover.h",
     "ios_chrome_browsing_data_remover.mm",
   ]

ios/chrome/browser/browsing_data/browsing_data_removal_controller.h

@@ -21,9 +21,9 @@ class ChromeBrowserState;
 // ChromeBrowserState.
 @interface BrowsingDataRemovalController : NSObject
 
-// Removes browsing data from |browserState| for datatypes in |mask|.
-// |mask| is obtained from IOSChromeBrowsingDataRemover::RemoveDataMask.
-// |browserState| cannot be null and must not be off the record.
+// Removes browsing data from |browserState| for datatypes in |mask|. |mask| is
+// obtained from BrowsingDataRemoveMask. |browserState| cannot be null and must
+// not be off the record.
 - (void)removeBrowsingDataFromBrowserState:
             (ios::ChromeBrowserState*)browserState
                                       mask:(BrowsingDataRemoveMask)mask
@@ -31,11 +31,10 @@ class ChromeBrowserState;
                          completionHandler:(ProceduralBlock)completionHandler;
 
 // Removes browsing data that iOS has associated with |browserState| and which
-// is not removed when the |browserState| is destroyed.
-// |mask| is obtained from IOSChromeBrowsingDataRemover::RemoveDataMask
-// |browserState| cannot be  null. |completionHandler| is called when this
-// operation finishes. This method finishes removal of the browsing data even if
-// |browserState| is destroyed after this method call.
+// is not removed when the |browserState| is destroyed. |mask| is obtained from
+// BrowsingDataRemoveMask. |browserState| cannot be null. |completionHandler| is
+// called when this operation finishes. This method finishes removal of the
+// browsing data even if |browserState| is destroyed after this method call.
 - (void)
 removeIOSSpecificIncognitoBrowsingDataFromBrowserState:
     (ios::ChromeBrowserState*)browserState

ios/chrome/browser/browsing_data/browsing_data_removal_controller.mm

@@ -21,7 +21,6 @@
 #include "components/signin/ios/browser/account_consistency_service.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #include "ios/chrome/browser/browsing_data/browsing_data_remove_mask.h"
-#include "ios/chrome/browser/browsing_data/browsing_data_remover_helper.h"
 #include "ios/chrome/browser/browsing_data/ios_chrome_browsing_data_remover.h"
 #include "ios/chrome/browser/sessions/session_util.h"
 #include "ios/chrome/browser/signin/account_consistency_service_factory.h"
@@ -48,12 +47,11 @@ void DoNothing(uint32_t n) {}
 
 @interface BrowsingDataRemovalController ()
 // Removes browsing data that is created by web views associated with
-// |browserState|. |mask| is obtained from
-// IOSChromeBrowsingDataRemover::RemoveDataMask. |deleteBegin| defines the begin
-// time from which the data has to be removed, up to the present time.
-// |completionHandler| is called when this operation finishes. This method
-// finishes removal of the browsing data even if |browserState| is destroyed
-// after this method call.
+// |browserState|. |mask| is obtained from BrowsingDataRemoveMask. |deleteBegin|
+// defines the begin time from which the data has to be removed, up to the
+// present time. |completionHandler| is called when this operation finishes.
+// This method finishes removal of the browsing data even if |browserState| is
+// destroyed after this method call.
 - (void)
 removeWebViewCreatedBrowsingDataFromBrowserState:
     (ios::ChromeBrowserState*)browserState
@@ -63,12 +61,10 @@ removeWebViewCreatedBrowsingDataFromBrowserState:
                                    (ProceduralBlock)completionHandler;
 // Removes browsing data that is created by WKWebViews associated with
 // |browserState|. |browserState| must not be off the record. |mask| is obtained
-// from IOSChromeBrowsingDataRemover::RemoveDataMask. |deleteBegin| defines the
-// begin time from which the data has to be removed, up to the present time.
-// |completionHandler| is called when this operation finishes. This method
-// finishes removal of the browsing data even if |browserState| is destroyed
-// after this method call.
-// Note: This method works only on iOS9+.
+// from BrowsingDataRemoveMask. |deleteBegin| defines the begin time from which
+// the data has to be removed, up to the present time. |completionHandler| is
+// called when this operation finishes. This method finishes removal of the
+// browsing data even if |browserState| is destroyed after this method call.
 - (void)
 removeWKWebViewCreatedBrowsingDataFromBrowserState:
     (ios::ChromeBrowserState*)browserState
@@ -78,12 +74,11 @@ removeWKWebViewCreatedBrowsingDataFromBrowserState:
                                      (ProceduralBlock)completionHandler;
 
 // Removes browsing data associated with |browserState| that is specific to iOS
-// and not removed when the |browserState| is destroyed.
-// |mask| is obtained from IOSChromeBrowsingDataRemover::RemoveDataMask
-// |deleteBegin| defines the begin time from which the data has to be removed.
-// |browserState| cannot be  null. |completionHandler| is called when
-// this operation finishes. This method finishes removal of the browsing data
-// even if |browserState| is destroyed after this method call.
+// and not removed when the |browserState| is destroyed. |mask| is obtained from
+// BrowsingDataRemoveMask |deleteBegin| defines the begin time from which the
+// data has to be removed. |browserState| cannot be  null. |completionHandler|
+// is called when this operation finishes. This method finishes removal of the
+// browsing data even if |browserState| is destroyed after this method call.
 - (void)
 removeIOSSpecificBrowsingDataFromBrowserState:
     (ios::ChromeBrowserState*)browserState
@@ -91,11 +86,10 @@ removeIOSSpecificBrowsingDataFromBrowserState:
                                   deleteBegin:(base::Time)deleteBegin
                             completionHandler:
                                 (ProceduralBlock)completionHandler;
-// Removes browsing data from |browserState| that is persisted on disk.
-// |mask| is obtained from IOSChromeBrowsingDataRemover::RemoveDataMask.
-// |browserState| cannot be null and must be off the record.
-// This method finishes removal of the browsing data even if |browserState| is
-// destroyed after this method call.
+// Removes browsing data from |browserState| that is persisted on disk. |mask|
+// is obtained from BrowsingDataRemoveMask. |browserState| cannot be null and
+// must be off the record. This method finishes removal of the browsing data
+// even if |browserState| is destroyed after this method call.
 - (void)
 removeIOSSpecificPersistentIncognitoDataFromBrowserState:
     (ios::ChromeBrowserState*)browserState
@@ -120,19 +114,14 @@ removeIOSSpecificPersistentIncognitoDataFromBrowserState:
 @end
 
 @implementation BrowsingDataRemovalController {
-  // Wrapper around IOSChromeBrowsingDataRemover that serializes removal
-  // operations.
-  std::unique_ptr<BrowsingDataRemoverHelper> _browsingDataRemoverHelper;
+  // Mapping from ChromeBrowserState to the IOSChromeBrowsingDataRemover used
+  // for removal of the data on that instance.
+  base::flat_map<ios::ChromeBrowserState*,
+                 std::unique_ptr<IOSChromeBrowsingDataRemover>>
+      _browingDataRemovers;
   // A map that tracks the number of pending removals for a given
   // ChromeBrowserState.
-  base::hash_map<ios::ChromeBrowserState*, int> _pendingRemovalCount;
-}
-
-- (instancetype)init {
-  if ((self = [super init])) {
-    _browsingDataRemoverHelper.reset(new BrowsingDataRemoverHelper());
-  }
-  return self;
+  base::flat_map<ios::ChromeBrowserState*, int> _pendingRemovalCount;
 }
 
 - (void)removeBrowsingDataFromBrowserState:
@@ -189,10 +178,19 @@ removeIOSSpecificPersistentIncognitoDataFromBrowserState:
 
   if (!browserState->IsOffTheRecord()) {
     callbackCounter->IncrementCount();
-    _browsingDataRemoverHelper->Remove(browserState, mask, timePeriod,
-                                       base::BindBlockArc(^{
-                                         callbackCounter->DecrementCount();
-                                       }));
+    auto iterator = _browingDataRemovers.find(browserState);
+    if (iterator == _browingDataRemovers.end()) {
+      iterator =
+          _browingDataRemovers
+              .emplace(
+                  browserState,
+                  std::make_unique<IOSChromeBrowsingDataRemover>(browserState))
+              .first;
+      DCHECK(iterator != _browingDataRemovers.end());
+    }
+    iterator->second->Remove(timePeriod, mask, base::BindBlockArc(^{
+                               callbackCounter->DecrementCount();
+                             }));
   }
 }
 
@@ -301,8 +299,7 @@ removeWKWebViewCreatedBrowsingDataFromBrowserState:
     callbackCounter->DecrementCount();
   };
 
-  // Converts browsing data types from
-  // IOSChromeBrowsingDataRemover::RemoveDataMask to
+  // Converts browsing data types from BrowsingDataRemoveMask to
   // WKWebsiteDataStore strings.
   NSMutableSet* dataTypesToRemove = [[NSMutableSet alloc] init];
   if (IsRemoveDataMaskSet(mask, BrowsingDataRemoveMask::REMOVE_CACHE_STORAGE)) {
@@ -444,6 +441,7 @@ removeIOSSpecificPersistentIncognitoDataFromBrowserState:
 }
 
 - (void)browserStateDestroyed:(ios::ChromeBrowserState*)browserState {
+  _browingDataRemovers.erase(browserState);
   _pendingRemovalCount.erase(browserState);
 }
 

ios/chrome/browser/browsing_data/browsing_data_remover_helper.cc

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "ios/chrome/browser/browsing_data/browsing_data_remover_helper.h"
-
-#include <utility>
-
-#include "ios/chrome/browser/browser_state/chrome_browser_state.h"
-
-BrowsingDataRemoverHelper::BrowsingDataRemoverHelper()
-    : current_remover_(nullptr) {}
-
-BrowsingDataRemoverHelper::~BrowsingDataRemoverHelper() {
-  DCHECK(pending_removals_.empty());
-}
-
-BrowsingDataRemoverHelper::BrowsingDataRemovalInfo::BrowsingDataRemovalInfo(
-    BrowsingDataRemoveMask remove_mask,
-    browsing_data::TimePeriod time_period,
-    const base::Closure& callback)
-    : remove_mask(remove_mask), time_period(time_period) {
-  callbacks.push_back(callback);
-}
-
-BrowsingDataRemoverHelper::BrowsingDataRemovalInfo::~BrowsingDataRemovalInfo() {
-}
-
-void BrowsingDataRemoverHelper::Remove(ios::ChromeBrowserState* browser_state,
-                                       BrowsingDataRemoveMask remove_mask,
-                                       browsing_data::TimePeriod time_period,
-                                       const base::Closure& callback) {
-  DCHECK(browser_state);
-  DCHECK(!browser_state->IsOffTheRecord());
-  // IOSChromeBrowsingDataRemover::Callbacks are called before
-  // OnIOSChromeBrowsingDataRemoverDone() and after
-  // IOSChromeBrowsingDataRemover::is_removing() is set to false. In this
-  // window, |current_remover_| needs to be checked as well.
-  if (current_remover_ || IOSChromeBrowsingDataRemover::is_removing()) {
-    // IOSChromeBrowsingDataRemover is not re-entrant. If it is already running,
-    // add the browser_state to |pending_removals_| for later deletion. If the
-    // browser_state is already scheduled for removal of browsing data, update
-    // the remove mask and callbacks.
-    DCHECK(current_remover_);
-    auto pending_removals_iter = pending_removals_.find(browser_state);
-    if (pending_removals_iter == pending_removals_.end()) {
-      std::unique_ptr<BrowsingDataRemovalInfo> removal_info(
-          new BrowsingDataRemovalInfo(remove_mask, time_period, callback));
-      pending_removals_[browser_state] = std::move(removal_info);
-    } else {
-      pending_removals_iter->second->remove_mask |= remove_mask;
-      pending_removals_iter->second->callbacks.push_back(callback);
-    }
-  } else {
-    std::unique_ptr<BrowsingDataRemovalInfo> removal_info(
-        new BrowsingDataRemovalInfo(remove_mask, time_period, callback));
-    DoRemove(browser_state, std::move(removal_info));
-  }
-}
-
-void BrowsingDataRemoverHelper::OnIOSChromeBrowsingDataRemoverDone() {
-  current_remover_ = nullptr;
-
-  DCHECK(current_removal_info_);
-  // Inform clients of the currently finished removal operation that browsing
-  // data was removed.
-  for (const auto& callback : current_removal_info_->callbacks) {
-    if (!callback.is_null()) {
-      callback.Run();
-    }
-  }
-  current_removal_info_.reset();
-
-  if (pending_removals_.empty())
-    return;
-
-  ios::ChromeBrowserState* next_browser_state =
-      pending_removals_.begin()->first;
-  std::unique_ptr<BrowsingDataRemovalInfo> removal_info =
-      std::move(pending_removals_[next_browser_state]);
-  pending_removals_.erase(next_browser_state);
-  DoRemove(next_browser_state, std::move(removal_info));
-}
-
-void BrowsingDataRemoverHelper::DoRemove(
-    ios::ChromeBrowserState* browser_state,
-    std::unique_ptr<BrowsingDataRemovalInfo> removal_info) {
-  DCHECK(!current_remover_ && !IOSChromeBrowsingDataRemover::is_removing());
-
-  current_removal_info_ = std::move(removal_info);
-
-  // IOSChromeBrowsingDataRemover deletes itself.
-  IOSChromeBrowsingDataRemover* remover =
-      IOSChromeBrowsingDataRemover::CreateForPeriod(
-          browser_state, current_removal_info_->time_period);
-  remover->AddObserver(this);
-  current_remover_ = remover;
-  BrowsingDataRemoveMask remove_mask = current_removal_info_->remove_mask;
-  remover->Remove(remove_mask);
-}

ios/chrome/browser/browsing_data/browsing_data_remover_helper.h

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef IOS_CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_REMOVER_HELPER_H_
-#define IOS_CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_REMOVER_HELPER_H_
-
-#include <map>
-#include <memory>
-#include <vector>
-
-#include "base/callback.h"
-#include "ios/chrome/browser/browsing_data/browsing_data_remove_mask.h"
-#include "ios/chrome/browser/browsing_data/ios_chrome_browsing_data_remover.h"
-
-namespace ios {
-class ChromeBrowserState;
-}
-
-// A helper class that serializes execution of IOSChromeBrowsingDataRemover
-// methods since the IOSChromeBrowsingDataRemover APIs are not re-entrant.
-class BrowsingDataRemoverHelper
-    : public IOSChromeBrowsingDataRemover::Observer {
- public:
-  BrowsingDataRemoverHelper();
-  ~BrowsingDataRemoverHelper() override;
-
-  // Removes the specified browsing data associated with |browser_state|. Calls
-  // |callback| when the browsing data is actually removed. |browser_state|
-  // cannot be null and must not be off the record.
-  // |callback| is called on the main thread.
-  // Note: Removal operations are not necessarily processed in the sequence that
-  // they are received in.
-  void Remove(ios::ChromeBrowserState* browser_state,
-              BrowsingDataRemoveMask remove_mask,
-              browsing_data::TimePeriod time_period,
-              const base::Closure& callback);
-
- private:
-  // Encapsulates the information that is needed to remove browsing data from
-  // a ChromeBrowserState.
-  struct BrowsingDataRemovalInfo {
-    // Creates a BrowsingDataRemovalInfo with a single callback |callback|.
-    BrowsingDataRemovalInfo(BrowsingDataRemoveMask remove_mask,
-                            browsing_data::TimePeriod time_period,
-                            const base::Closure& callback);
-    ~BrowsingDataRemovalInfo();
-    // The mask of all the types of browsing data that needs to be removed.
-    BrowsingDataRemoveMask remove_mask;
-    // Time period for which the user wants to remove the data.
-    browsing_data::TimePeriod time_period;
-    // The vector of callbacks that need to be run when browsing data is
-    // actually removed.
-    std::vector<base::Closure> callbacks;
-  };
-
-  // IOSChromeBrowsingDataRemover::Observer methods.
-  void OnIOSChromeBrowsingDataRemoverDone() override;
-
-  // Removes the browsing data using IOSChromeBrowsingDataRemover.
-  // IOSChromeBrowsingDataRemover
-  // must not be running.
-  void DoRemove(ios::ChromeBrowserState* browser_state,
-                std::unique_ptr<BrowsingDataRemovalInfo> removal_info);
-
-  // A map that contains the all the ChromeBrowserStates that have a removal
-  // operation pending along with their associated BrowsingDataRemovalInfo.
-  std::map<ios::ChromeBrowserState*, std::unique_ptr<BrowsingDataRemovalInfo>>
-      pending_removals_;
-  // The BrowsingDataRemovalInfo of the currently enqueued removal operation.
-  std::unique_ptr<BrowsingDataRemovalInfo> current_removal_info_;
-  // The actual object that perfoms the removal of browsing data.
-  IOSChromeBrowsingDataRemover* current_remover_;
-};
-
-#endif  // IOS_CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_REMOVER_HELPER_H_

ios/chrome/browser/browsing_data/ios_chrome_browsing_data_remover.h

@@ -5,24 +5,19 @@
 #ifndef IOS_CHROME_BROWSER_BROWSING_DATA_IOS_CHROME_BROWSING_DATA_REMOVER_H_
 #define IOS_CHROME_BROWSER_BROWSING_DATA_IOS_CHROME_BROWSING_DATA_REMOVER_H_
 
-#include <stdint.h>
-
 #include <memory>
-#include <set>
 
 #include "base/callback.h"
+#include "base/containers/queue.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
-#include "base/observer_list.h"
-#include "base/sequenced_task_runner_helpers.h"
+#include "base/sequence_checker.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "base/time/time.h"
 #include "components/browsing_data/core/browsing_data_utils.h"
 #include "components/prefs/pref_member.h"
 #include "components/search_engines/template_url_service.h"
 #include "ios/chrome/browser/browsing_data/browsing_data_remove_mask.h"
-#include "url/gurl.h"
-#include "url/origin.h"
 
 namespace ios {
 class ChromeBrowserState;
@@ -34,73 +29,60 @@ class URLRequestContextGetter;
 
 // IOSChromeBrowsingDataRemover is responsible for removing data related to
 // browsing: visits in url database, downloads, cookies ...
-
 class IOSChromeBrowsingDataRemover {
  public:
-  // This value is here to allow compilation of downstream code. It will be
-  // removed once downstream code has been fixed to use BrowsingDataRemoveMask.
-  const BrowsingDataRemoveMask REMOVE_ALL = BrowsingDataRemoveMask::REMOVE_ALL;
-
-  // Observer is notified when the removal is done. Done means keywords have
-  // been deleted, cache cleared and all other tasks scheduled.
-  class Observer {
-   public:
-    virtual void OnIOSChromeBrowsingDataRemoverDone() = 0;
-
-   protected:
-    virtual ~Observer() {}
-  };
-
-  // Creates a IOSChromeBrowsingDataRemover bound to a specific period of time
-  // (as defined via a TimePeriod). Returns a raw pointer, as
-  // IOSChromeBrowsingDataRemover retains ownership of itself, and deletes
-  // itself once finished.
-  static IOSChromeBrowsingDataRemover* CreateForPeriod(
-      ios::ChromeBrowserState* browser_state,
-      browsing_data::TimePeriod period);
-
-  // Is the IOSChromeBrowsingDataRemover currently in the process of removing
-  // data?
-  static bool is_removing() { return is_removing_; }
+  // Creates a IOSChromeBrowsingDataRemover to remove browser data from the
+  // specified ChromeBrowserstate. Use Remove to initiate the removal.
+  explicit IOSChromeBrowsingDataRemover(ios::ChromeBrowserState* browser_state);
+  ~IOSChromeBrowsingDataRemover();
 
-  // Removes the specified items related to browsing for all origins.
-  void Remove(BrowsingDataRemoveMask mask);
+  // Is the object currently in the process of removing data?
+  bool is_removing() { return is_removing_; }
 
-  void AddObserver(Observer* observer);
-  void RemoveObserver(Observer* observer);
+  // Removes browsing data for the given |time_range| with data types specified
+  // by |remove_mask|. The |callback| is invoked asynchronously when the data
+  // has been removed.
+  void Remove(browsing_data::TimePeriod time_period,
+              BrowsingDataRemoveMask remove_mask,
+              base::OnceClosure callback);
 
  private:
+  // Represents a single removal task. Contains all parameters to execute it.
+  struct RemovalTask {
+    RemovalTask(base::Time delete_begin,
+                base::Time delete_end,
+                BrowsingDataRemoveMask mask,
+                base::OnceClosure callback);
+    RemovalTask(RemovalTask&& other) noexcept;
+    ~RemovalTask();
+
+    base::Time delete_begin;
+    base::Time delete_end;
+    BrowsingDataRemoveMask mask;
+    base::OnceClosure callback;
+  };
+
   // Setter for |is_removing_|; DCHECKs that we can only start removing if we're
   // not already removing, and vice-versa.
-  static void set_removing(bool is_removing);
-
-  // Creates a IOSChromeBrowsingDataRemover to remove browser data from the
-  // specified profile in the specified time range. Use Remove to initiate the
-  // removal.
-  IOSChromeBrowsingDataRemover(ios::ChromeBrowserState* browser_state,
-                               base::Time delete_begin,
-                               base::Time delete_end);
-
-  // IOSChromeBrowsingDataRemover deletes itself (using DeleteHelper) and is
-  // not supposed to be deleted by other objects so make destructor private and
-  // DeleteHelper a friend.
-  friend class base::DeleteHelper<IOSChromeBrowsingDataRemover>;
-
-  ~IOSChromeBrowsingDataRemover();
+  void SetRemoving(bool is_removing);
 
   // Callback for when TemplateURLService has finished loading. Clears the data,
   // and invoke the callback.
-  void OnKeywordsLoaded(base::OnceClosure callback);
+  void OnKeywordsLoaded(base::Time delete_begin,
+                        base::Time delete_end,
+                        base::OnceClosure callback);
 
-  // Removes the specified items related to browsing for a specific host. If the
-  // provided |remove_url| is empty, data is removed for all origins.
-  // TODO(mkwst): The current implementation relies on unique (empty) origins to
-  // signal removal of all origins. Reconsider this behavior if/when we build
-  // a "forget this site" feature.
-  void RemoveImpl(BrowsingDataRemoveMask mask);
+  // Execute the next removal task. Called after the previous task was finished
+  // or directly from Remove.
+  void RunNextTask();
 
-  // Notifies observers and deletes this object.
-  void NotifyAndDelete();
+  // Removes the specified items related to browsing.
+  void RemoveImpl(base::Time delete_begin,
+                  base::Time delete_end,
+                  BrowsingDataRemoveMask mask);
+
+  // Invokes the current task callback that the removal has completed.
+  void NotifyRemovalComplete();
 
   // Called by the closures returned by CreatePendingTaskCompletionClosure().
   // Checks if all tasks have completed, and if so, calls Notify().
@@ -115,28 +97,23 @@ class IOSChromeBrowsingDataRemover {
   // purposes.
   base::WeakPtr<IOSChromeBrowsingDataRemover> GetWeakPtr();
 
-  // ChromeBrowserState we're to remove from.
-  ios::ChromeBrowserState* browser_state_;
-
-  // Start time to delete from.
-  const base::Time delete_begin_;
-
-  // End time to delete to.
-  base::Time delete_end_;
+  // This object is sequence affine.
+  SEQUENCE_CHECKER(sequence_checker_);
 
-  // True if Remove has been invoked.
-  static bool is_removing_;
+  // ChromeBrowserState we're to remove from.
+  ios::ChromeBrowserState* browser_state_ = nullptr;
 
   // Used to delete data from HTTP cache.
-  scoped_refptr<net::URLRequestContextGetter> main_context_getter_;
+  scoped_refptr<net::URLRequestContextGetter> context_getter_;
+
+  // Is the object currently in the process of removing data?
+  bool is_removing_ = false;
 
   // Number of pending tasks.
   int pending_tasks_count_ = 0;
 
-  // The removal mask for the current removal operation.
-  BrowsingDataRemoveMask remove_mask_ = BrowsingDataRemoveMask::REMOVE_NOTHING;
-
-  base::ObserverList<Observer> observer_list_;
+  // Removal tasks to be processed.
+  base::queue<RemovalTask> removal_queue_;
 
   // Used if we need to clear history.
   base::CancelableTaskTracker history_task_tracker_;