Update from https://crrev.com/333737

base/metrics/histogram_base.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_METRICS_HISTOGRAM_BASE_H_
 #define BASE_METRICS_HISTOGRAM_BASE_H_
 
 #include <stdint.h>
 
 #include <string>
 #include <vector>
 
 #include "base/atomicops.h"
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string_piece.h"
 #include "base/time/time.h"
 
-class Pickle;
-class PickleIterator;
-
 namespace base {
 
 class DictionaryValue;
 class HistogramBase;
 class HistogramSamples;
 class ListValue;
+class Pickle;
+class PickleIterator;
 
 ////////////////////////////////////////////////////////////////////////////////
 // These enums are used to facilitate deserialization of histograms from other
 // processes into the browser. If you create another class that inherits from
 // HistogramBase, add new histogram types and names below.
 
 enum BASE_EXPORT HistogramType {
   HISTOGRAM,
   LINEAR_HISTOGRAM,
   BOOLEAN_HISTOGRAM,
   CUSTOM_HISTOGRAM,
   SPARSE_HISTOGRAM,
 };
 
 std::string HistogramTypeToString(HistogramType type);
 
 // Create or find existing histogram that matches the pickled info.
 // Returns NULL if the pickled data has problems.
 BASE_EXPORT_PRIVATE HistogramBase* DeserializeHistogramInfo(
-    PickleIterator* iter);
+    base::PickleIterator* iter);
 
 ////////////////////////////////////////////////////////////////////////////////
 
 class BASE_EXPORT HistogramBase {
  public:
   typedef int32_t Sample;                // Used for samples.
   typedef subtle::Atomic32 AtomicCount;  // Used to count samples.
   typedef int32_t Count;  // Used to manipulate counts in temporaries.
 
   static const Sample kSampleType_MAX;  // INT_MAX
@@ skipping 55 matching lines @@
                                         Sample expected_maximum,
                                         size_t expected_bucket_count) const = 0;
 
   virtual void Add(Sample value) = 0;
 
   // 2 convenient functions that call Add(Sample).
   void AddTime(const TimeDelta& time);
   void AddBoolean(bool value);
 
   virtual void AddSamples(const HistogramSamples& samples) = 0;
-  virtual bool AddSamplesFromPickle(PickleIterator* iter) = 0;
+  virtual bool AddSamplesFromPickle(base::PickleIterator* iter) = 0;
 
   // Serialize the histogram info into |pickle|.
   // Note: This only serializes the construction arguments of the histogram, but
   // does not serialize the samples.
-  bool SerializeInfo(Pickle* pickle) const;
+  bool SerializeInfo(base::Pickle* pickle) const;
 
   // Try to find out data corruption from histogram and the samples.
   // The returned value is a combination of Inconsistency enum.
   virtual int FindCorruption(const HistogramSamples& samples) const;
 
   // Snapshot the current complete set of sample data.
   // Override with atomic/locked snapshot if needed.
   virtual scoped_ptr<HistogramSamples> SnapshotSamples() const = 0;
 
   // The following methods provide graphical histogram displays.
   virtual void WriteHTMLGraph(std::string* output) const = 0;
   virtual void WriteAscii(std::string* output) const = 0;
 
   // Produce a JSON representation of the histogram. This is implemented with
   // the help of GetParameters and GetCountAndBucketData; overwrite them to
   // customize the output.
   void WriteJSON(std::string* output) const;
 
  protected:
   // Subclasses should implement this function to make SerializeInfo work.
-  virtual bool SerializeInfoImpl(Pickle* pickle) const = 0;
+  virtual bool SerializeInfoImpl(base::Pickle* pickle) const = 0;
 
   // Writes information about the construction parameters in |params|.
   virtual void GetParameters(DictionaryValue* params) const = 0;
 
   // Writes information about the current (non-empty) buckets and their sample
   // counts to |buckets|, the total sample count to |count| and the total sum
   // to |sum|.
   virtual void GetCountAndBucketData(Count* count,
                                      int64* sum,
                                      ListValue* buckets) const = 0;
@@ skipping 15 matching lines @@
  private:
   const std::string histogram_name_;
   int32_t flags_;
 
   DISALLOW_COPY_AND_ASSIGN(HistogramBase);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_BASE_H_