Add a Java API for UMA histograms.

base/android/java/src/org/chromium/base/metrics/RecordHistogram.java

Index: base/android/java/src/org/chromium/base/metrics/RecordHistogram.java
diff --git a/base/android/java/src/org/chromium/base/metrics/RecordHistogram.java b/base/android/java/src/org/chromium/base/metrics/RecordHistogram.java
new file mode 100644
index 0000000000000000000000000000000000000000..8295a850c0aabaf1b0cd60bd80faf565c70b081e
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+++ b/base/android/java/src/org/chromium/base/metrics/RecordHistogram.java
@@ -0,0 +1,62 @@
+// 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.metrics;
+
+import org.chromium.base.JNINamespace;
+import org.chromium.base.VisibleForTesting;
+
+/**
+ * Java API for recording UMA histograms. As opposed to macros used in native code, these calls are
+ * not caching the histogram pointer; also, the JNI calls are relatively costly - avoid calling
+ * these methods in performance-critical code.
+ */
+@JNINamespace("base::android")
+public class RecordHistogram {
+    /**
+     * Records a sample in a boolean UMA histogram of the given name. Boolean histogram has two
+     * buckets, corresponding to success (true) and failure (false).
+     * @param name name of the histogram
+     * @param sample sample to be recorded, either true or false
+     */
+    public static void recordBooleanHistogram(String name, boolean sample) {
+        nativeRecordBooleanHistogram(name, sample);
+    }
+
+    /**
+     * Records a sample in an enumerated histogram of the given name and boundary. Note that
+     * |boundary| identifies the histogram - it should be the same at every invocation.
+     * @param name name of the histogram
+     * @param sample sample to be recorded, at least 0 and at most |boundary| - 1
+     * @param boundary upper bound for legal sample values - all sample values has to be strictly
+     *        lower than |boundary|
+     */
+    public static void recordEnumeratedHistogram(String name, int sample, int boundary) {
+        nativeRecordEnumeratedHistogram(name, sample, boundary);
+    }
+
+    /**
+     * Returns the number of samples recorded in the given bucket of the given histogram.
+     * @param name name of the histogram to look up
+     * @param sample the bucket containing this sample value will be looked up
+     */
+    @VisibleForTesting
+    public static int getHistogramValueCountForTesting(String name, int sample) {
+        return nativeGetHistogramValueCountForTesting(name, sample);
+    }
+
+    /**
+     * Initializes the metrics system.
+     */
+    public static void initialize() {
+        nativeInitialize();
+    }
+
+    private static native void nativeRecordBooleanHistogram(String name, boolean sample);
+    private static native void nativeRecordEnumeratedHistogram(
+            String name, int sample, int boundary);
+
+    private static native int nativeGetHistogramValueCountForTesting(String name, int sample);
+    private static native void nativeInitialize();
+}