Polish the result communication and display of the browsing data counters.

chrome/browser/browsing_data/browsing_data_counter.h

 // Copyright (c) 2015 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_COUNTER_H_
 #define CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_COUNTER_H_
 
 #include <stdint.h>
 #include <string>
 
 #include "base/callback.h"
+#include "base/macros.h"
 #include "base/prefs/pref_member.h"
 #include "chrome/browser/browsing_data/browsing_data_remover.h"
 #include "chrome/browser/profiles/profile.h"
 
 class BrowsingDataCounter {
  public:
-  typedef uint64_t ResultInt;
-  typedef base::Callback<void(bool, ResultInt)> Callback;
+  typedef int64_t ResultInt;
+
+  // Base class of results returned by BrowsingDataCounter. When the computation
+  // has started, an instance is returned to represent a pending result.
+  class Result {
+   public:
+    explicit Result(const BrowsingDataCounter* source);
+    virtual ~Result();
+
+    const BrowsingDataCounter* source() const { return source_; }
+    virtual bool Finished() const;
+
+   private:
+    const BrowsingDataCounter* source_;
+
+    DISALLOW_COPY_AND_ASSIGN(Result);
+  };
+
+  // A subclass of Result returned when the computation has finished. The result
+  // value can be retrieved by calling |Value()|. Some BrowsingDataCounter
+  // subclasses might use a subclass of FinishedResult to provide more complex
+  // results.
+  class FinishedResult : public Result {
+   public:
+    FinishedResult(const BrowsingDataCounter* source, ResultInt value);
+    ~FinishedResult() override;
+
+    // Result:
+    bool Finished() const override;
+
+    ResultInt Value() const;
+
+   private:
+    ResultInt value_;
+
+    DISALLOW_COPY_AND_ASSIGN(FinishedResult);
+  };
+
+  typedef base::Callback<void(scoped_ptr<Result>)> Callback;
 
   BrowsingDataCounter();
   virtual ~BrowsingDataCounter();
 
   // Should be called once to initialize this class.
   void Init(Profile* profile,
             const Callback& callback);
 
   // Name of the preference associated with this counter.
   virtual const std::string& GetPrefName() const = 0;
 
   // The profile associated with this counter.
   Profile* GetProfile() const;
 
   // Restarts the counter. Will be called automatically if the counting needs
   // to be restarted, e.g. when the deletion preference changes state or when
   // we are notified of data changes.
   void Restart();
 
  protected:
   // Should be called from |Count| by any overriding class to indicate that
-  // counting is finished and report the |result|.
-  void ReportResult(ResultInt result);
+  // counting is finished and report |value| as the result.
+  void ReportResult(ResultInt value);
+
+  // A convenience overload of the previous method that allows subclasses to
+  // provide a custom |result|.
+  void ReportResult(scoped_ptr<Result> result);
 
   // Calculates the beginning of the counting period as |period_| before now.
   base::Time GetPeriodStart();
 
  private:
   // Called after the class is initialized by calling |Init|.
   virtual void OnInitialized();
 
   // Count the data.
   virtual void Count() = 0;
@@ skipping 11 matching lines @@
 
   // The integer preference describing the time period for which this data type
   // is to be deleted.
   IntegerPrefMember period_;
 
   // Whether this class was properly initialized by calling |Init|.
   bool initialized_ = false;
 };
 
 #endif  // CHROME_BROWSER_BROWSING_DATA_BROWSING_DATA_COUNTER_H_