Add a Java API for UMA histograms.

base/test/android/javatests/src/org/chromium/base/test/util/MetricsUtils.java

Index: base/test/android/javatests/src/org/chromium/base/test/util/MetricsUtils.java
diff --git a/base/test/android/javatests/src/org/chromium/base/test/util/MetricsUtils.java b/base/test/android/javatests/src/org/chromium/base/test/util/MetricsUtils.java
new file mode 100644
index 0000000000000000000000000000000000000000..c4664d68b0a22a594ab307ed267958de0ca105eb
--- /dev/null
+++ b/base/test/android/javatests/src/org/chromium/base/test/util/MetricsUtils.java
@@ -0,0 +1,43 @@
+// Copyright 2014 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.
+
+package org.chromium.base.test.util;
+
+import org.chromium.base.metrics.RecordHistogram;
+
+/**
+ * Helpers for testing UMA metrics.
+ */
+public class MetricsUtils {
+    /**
+     * Helper class that snapshots the given bucket of the given UMA histogram on its creation,
+     * allowing to inspect the number of samples recorded during its lifetime.
+     */
+    public static class HistogramDelta {
+        private final String mHistogram;
+        private final int mSampleValue;
+
+        private final int mInitialCount;
+
+        private int get() {
+            return RecordHistogram.getHistogramValueCountForTesting(mHistogram, mSampleValue);
+        }
+
+        /**
+         * Snapshots the given bucket of the given histogram.
+         * @param histogram name of the histogram to snapshot
+         * @param sampleValue the bucket that contains this value will be snapshot
+         */
+        public HistogramDelta(String histogram, int sampleValue) {
+            mHistogram = histogram;
+            mSampleValue = sampleValue;
+            mInitialCount = get();
+        }
+
+        /** Returns the number of samples of the snapshot bucket recorded since creation */
+        public int getDelta() {
+            return get() - mInitialCount;
+        }
+    }
+}