[MD settings] disable clear browsing data while it is running

chrome/browser/browsing_data/browsing_data_remover.h

 // Copyright (c) 2012 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 CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_REMOVER_H_
 #define CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_REMOVER_H_
 
 #include <stdint.h>
 
 #include <set>
@@ skipping 157 matching lines @@
     int origin_type_mask;
   };
 
   struct TimeRange {
     TimeRange(base::Time begin, base::Time end) : begin(begin), end(end) {}
 
     base::Time begin;
     base::Time end;
   };
 
-  // Observer is notified when the removal is done. Done means keywords have
-  // been deleted, cache cleared and all other tasks scheduled.
+  // Observer is notified when the removal is active and when it's done.
   class Observer {
    public:
+    // Whether removal is active. Note that not having an active removal is not
+    // same as completing a removal. That is why the removing status is separate
+    // from the done message.
+    virtual void OnBrowsingDataRemoving(bool is_removing) {}
+
+    // Done means keywords have been deleted, cache cleared and all other
+    // removal tasks are scheduled.
     virtual void OnBrowsingDataRemoverDone() = 0;
 
    protected:
     virtual ~Observer() {}
   };
 
   using Callback = base::Callback<void(const NotificationDetails&)>;
   using CallbackSubscription = std::unique_ptr<
       base::CallbackList<void(const NotificationDetails&)>::Subscription>;
 
@@ skipping 305 matching lines @@
   // not initialised, so the registry must be mocked out.
   std::unique_ptr<WebappRegistry> webapp_registry_;
 #endif
 
   base::WeakPtrFactory<BrowsingDataRemover> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowsingDataRemover);
 };
 
 #endif  // CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_REMOVER_H_