Add external data use observer

chrome/android/java/src/org/chromium/chrome/browser/datausage/ExternalDataUseObserverAndroid.java

Index: chrome/android/java/src/org/chromium/chrome/browser/datausage/ExternalDataUseObserverAndroid.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/datausage/ExternalDataUseObserverAndroid.java b/chrome/android/java/src/org/chromium/chrome/browser/datausage/ExternalDataUseObserverAndroid.java
new file mode 100644
index 0000000000000000000000000000000000000000..379abbf00b3cff0f1cfdfcbd8598284a1dba089b
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/datausage/ExternalDataUseObserverAndroid.java
@@ -0,0 +1,51 @@
+// Copyright 2015 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.chrome.browser.datausage;
+
+import android.content.Context;
+
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+import org.chromium.chrome.browser.ChromeApplication;
+import org.chromium.chrome.browser.util.NonThreadSafe;
+
+/**
+ * This class provides a base class implementation of a data use observer that is external to
+ * Chromium. This class is not thread safe.
+ */
+@JNINamespace("chrome::android")
+public class ExternalDataUseObserverAndroid {
+    private static final Object LOCK = new Object();
+    private static NonThreadSafe sThreadCheck = null;
+    private static ExternalDataUseObserverAndroid sExternalDataUseObserverAndroid;
+
+    @CalledByNative
+    private static ExternalDataUseObserverAndroid create(Context context, long nativePtr) {
+        synchronized (LOCK) {
+            if (sExternalDataUseObserverAndroid == null) {
+                assert sThreadCheck == null;
+                assert sExternalDataUseObserverAndroid == null;
+                sThreadCheck = new NonThreadSafe();
+
+                sExternalDataUseObserverAndroid =
+                        ((ChromeApplication) context)
+                                .createExternalDataUseObserverAndroid(nativePtr);
+            }
+        }
+        return sExternalDataUseObserverAndroid;
+    }
+
+    @CalledByNative
+    private void onDataUse(String tag, long bytesDownloaded, long bytesUploaded) {
+        assert sThreadCheck.calledOnValidThread();
+    }
+
+    /**
+     * Creates an instance of |@link #sExternalDataUseObserverAndroid}.
+     */
+    public ExternalDataUseObserverAndroid() {
+        assert sThreadCheck.calledOnValidThread();
+    }
+}