Make UMA stats creation available in the Java interface.

Only has counts stats right now but enumeration stats can easily be added in the future if needed.

BUG=webrtc:6313

Review-Url: https://codereview.webrtc.org/2320473002
Cr-Commit-Position: refs/heads/master@{#14146}

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

@@ -30,6 +30,8 @@ import java.util.Map;
 // 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");
   }
@@ -57,6 +59,36 @@ public class Metrics {
     }
   }
 
+  /**
+   * 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.addSample(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);
+    }
+
+    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);
   }