Add additional histograms with suffixes to ImportantFileWriter.

base/files/important_file_writer.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 BASE_FILES_IMPORTANT_FILE_WRITER_H_
 #define BASE_FILES_IMPORTANT_FILE_WRITER_H_
 
 #include <string>
 
 #include "base/base_export.h"
@@ skipping 35 matching lines @@
     // ImportantFileWriter has been created.
     virtual bool SerializeData(std::string* data) = 0;
 
    protected:
     virtual ~DataSerializer() {}
   };
 
   // Save |data| to |path| in an atomic manner. Blocks and writes data on the
   // current thread. Does not guarantee file integrity across system crash (see
   // the class comment above).
-  static bool WriteFileAtomically(const FilePath& path, StringPiece data);
+  static bool WriteFileAtomically(
+      const FilePath& path,
+      StringPiece data,
+      const std::string& histogram_suffix = std::string());

[dcheng, 2017/06/19 20:27:55]

OK, I misread the code and thought this was an internal helper.

As this is used by code outside ImportantFileWriter, this should be StringPIece
=/

Sorry for the churn. =(

[xaerox, 2017/06/20 04:21:00]

Done.

 
   // Initialize the writer.
   // |path| is the name of file to write.
   // |task_runner| is the SequencedTaskRunner instance where on which we will
   // execute file I/O operations.
   // All non-const methods, ctor and dtor must be called on the same thread.
   ImportantFileWriter(const FilePath& path,
-                      scoped_refptr<SequencedTaskRunner> task_runner);
+                      scoped_refptr<SequencedTaskRunner> task_runner,
+                      const char* histogram_suffix = nullptr);
 
   // Same as above, but with a custom commit interval.
   ImportantFileWriter(const FilePath& path,
                       scoped_refptr<SequencedTaskRunner> task_runner,
-                      TimeDelta interval);
+                      TimeDelta interval,
+                      const char* histogram_suffix = nullptr);
 
   // You have to ensure that there are no pending writes at the moment
   // of destruction.
   ~ImportantFileWriter();
 
   const FilePath& path() const { return path_; }
 
   // Returns true if there is a scheduled write pending which has not yet
   // been started.
   bool HasPendingWrite() const;
@@ skipping 56 matching lines @@
 
   // An override for |timer_| used for testing.
   Timer* timer_override_ = nullptr;
 
   // Serializer which will provide the data to be saved.
   DataSerializer* serializer_;
 
   // Time delta after which scheduled data will be written to disk.
   const TimeDelta commit_interval_;
 
+  // Custom histogram suffix.
+  const std::string histogram_suffix_;
+
   SEQUENCE_CHECKER(sequence_checker_);
 
   WeakPtrFactory<ImportantFileWriter> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ImportantFileWriter);
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_IMPORTANT_FILE_WRITER_H_