Add external data use observer

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

+// 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;
+
+/**
+ * This class provides a base class implementation of a data use observer that is external to
+ * Chromium. This class should be accessed only on IO thread.
+ */
+@JNINamespace("chrome::android")
+public class ExternalDataUseObserver {
+    /**
+     * Pointer to the native ExternalDataUseObserver object.
+     */
+    private long mNativeExternalDataUseObserver;
+
+    @CalledByNative
+    private static ExternalDataUseObserver create(Context context, long nativePtr) {
+        return ((ChromeApplication) context).createExternalDataUseObserver(nativePtr);
+    }
+
+    /*

[newt (away), 2015/10/14 00:02:48]

nit: use two asterisks "**"

[tbansal1, 2015/10/14 00:37:15]

Done.

+     * Notification that the native object has been destroyed.
+     */
+    @CalledByNative
+    private void onDestroy() {
+        mNativeExternalDataUseObserver = 0;
+    }
+
+    @CalledByNative
+    private void onDataUse(String tag, long bytesDownloaded, long bytesUploaded) {}
+
+    /**
+     * Creates an instance of {@link #ExternalDataUseObserver}.
+     */
+    public ExternalDataUseObserver(long nativePtr) {
+        mNativeExternalDataUseObserver = nativePtr;
+    }
+}