Merge multiple histogram snapshots into single one for reporting.

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 <limits.h>
 #include <stddef.h>
 #include <stdint.h>
@@ skipping 76 matching lines @@
     // memory segment has been created/attached, used to create a Persistent-
     // MemoryAllocator, and that loaded into the Histogram module before this
     // histogram is created.
     kIsPersistent = 0x40,
 
     // Only for Histogram and its sub classes: fancy bucket-naming support.
     kHexRangePrintingFlag = 0x8000,
   };
 
   // Histogram data inconsistency types.
-  enum Inconsistency {
+  enum Inconsistency : uint32_t {
     NO_INCONSISTENCIES = 0x0,
     RANGE_CHECKSUM_ERROR = 0x1,
     BUCKET_ORDER_ERROR = 0x2,
     COUNT_HIGH_ERROR = 0x4,
     COUNT_LOW_ERROR = 0x8,
 
-    NEVER_EXCEEDED_VALUE = 0x10
+    NEVER_EXCEEDED_VALUE = 0x10,
+
+    // This value is used only in HistogramSnapshotManager for marking
+    // internally when new inconsistencies are found.
+    NEW_INCONSISTENCY_FOUND = 0x8000000
   };
 
   explicit HistogramBase(const std::string& name);
   virtual ~HistogramBase();
 
   const std::string& histogram_name() const { return histogram_name_; }
 
   // Comapres |name| to the histogram name and triggers a DCHECK if they do not
   // match. This is a helper function used by histogram macros, which results in
   // in more compact machine code being generated by the macros.
@@ skipping 32 matching lines @@
   virtual void AddSamples(const HistogramSamples& samples) = 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(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;
+  virtual uint32_t 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;
 
+  // Calculate the change (delta) in histogram counts since the previous call
+  // to this method. Each successive call will return only those counts
+  // changed since the last call.
+  virtual scoped_ptr<HistogramSamples> SnapshotDelta() = 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:
@@ skipping 31 matching lines @@
  private:
   const std::string histogram_name_;
   AtomicCount flags_;
 
   DISALLOW_COPY_AND_ASSIGN(HistogramBase);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_BASE_H_