Make UMA stats creation available in the Java interface.

webrtc/api/android/java/src/org/webrtc/Metrics.java

 /*
  *  Copyright 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 12 matching lines @@
 //     |min|: 1
 //     |max|: 100
 //     |bucketCount|: 50
 //     |samples|: [30]:1
 //
 // Most histograms are not updated frequently (e.g. most video metrics are an
 // average over the call and recorded when a stream is removed).
 // The metrics can for example be retrieved when a peer connection is closed.
 
 public class Metrics {
+  private static final String TAG = "Metrics";
+
   static {
     System.loadLibrary("jingle_peerconnection_so");
   }
   public final Map<String, HistogramInfo> map =
        new HashMap<String, HistogramInfo>();  // <name, HistogramInfo>
 
   /**
    * Class holding histogram information.
    */
   public static class HistogramInfo {
     public final int min;
     public final int max;
     public final int bucketCount;
     public final Map<Integer, Integer> samples =
         new HashMap<Integer, Integer>();  // <value, # of events>
 
     public HistogramInfo(int min, int max, int bucketCount) {
       this.min = min;
       this.max = max;
       this.bucketCount = bucketCount;
     }
 
     public void addSample(int value, int numEvents) {
       samples.put(value, numEvents);
     }
   }
 
+  /**
+   * Class for holding the native pointer of a histogram. Since there is no way to destroy a
+   * histogram, please don't create unnecessary instances of this object. This class is thread safe.
+   *
+   * Usage example:
+   * private static final Histogram someMetricHistogram =
+   *     Histogram.createCounts("WebRTC.Video.SomeMetric", 1, 10000, 50);
+   * someMetricHistogram.addSampleLogged(someVariable);
+   */
+  static class Histogram {
+    private final long handle;
+    private final String name; // Only used for logging.
+
+    private Histogram(long handle, String name) {
+      this.handle = handle;
+      this.name = name;
+    }
+
+    static public Histogram createCounts(String name, int min, int max, int bucketCount) {
+      return new Histogram(nativeCreateCounts(name, min, max, bucketCount), name);
+    }
+
+    public void addSample(int sample) {
+      nativeAddSample(handle, sample);
+    }
+
+    public void addSampleLogged(int sample) {
+      Logging.d(TAG, "Add sample " + this.name + ": " + sample);
+      addSample(sample);
+    }
+
+    private static native long nativeCreateCounts(String name, int min, int max, int bucketCount);
+    private static native void nativeAddSample(long handle, int sample);
+  }
+
   private void add(String name, HistogramInfo info) {
     map.put(name, info);
   }
 
   // Enables gathering of metrics (which can be fetched with getAndReset()).
   // Must be called before PeerConnectionFactory is created.
   public static void enable() {
     nativeEnable();
   }
 
   // Gets and clears native histograms.
   public static Metrics getAndReset() {
     return nativeGetAndReset();
   }
 
   private static native void nativeEnable();
   private static native Metrics nativeGetAndReset();
 }