Android: Add API for getting native histograms.

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

Index: webrtc/api/java/src/org/webrtc/Metrics.java
diff --git a/webrtc/api/java/src/org/webrtc/Metrics.java b/webrtc/api/java/src/org/webrtc/Metrics.java
new file mode 100644
index 0000000000000000000000000000000000000000..90209ad062501bf25cfc2af945de02bba26516a8
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+++ b/webrtc/api/java/src/org/webrtc/Metrics.java
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+/*
+ *  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.
+ */
+
+package org.webrtc;
+
+import java.util.HashMap;
+import java.util.Map;
+
+// Java-side of androidmetrics_jni.cc.
+//
+// Rtc histograms can be queried through the API, getAndReset().
+// The returned map holds the name of a histogram and its samples.
+//
+// Example of |map| with one histogram:
+// |name|: "WebRTC.Video.InputFramesPerSecond"
+//     |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 {
+  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);
+    }
+  }
+
+  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();
+}