Add plumbing for accessing latest country in variations service in Java

chrome/android/java/src/org/chromium/chrome/browser/metrics/VariationsSession.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.metrics;
 
 import android.content.Context;
 
 import org.chromium.base.Callback;
 
@@ skipping 51 matching lines @@
 
     /**
      * Asynchronously returns the value of the "restrict" URL param that the variations service
      * should use for variation seed requests. This can be overriden by subclass to provide actual
      * restrict values, which must not be null.
      */
     protected void getRestrictMode(Context context, Callback<String> callback) {
         callback.onResult("");
     }
 
+    /**
+     * @return The latest country according to the current variations state.

[Alexei Svitkine (slow), 2017/04/19 21:42:57]

Expand comment to mention this could return null if not known.

[Yusuf, 2017/04/19 22:16:46]

Done.

+     */
+    public String getLatestCountry() {
+        return nativeGetLatestCountry();
+    }
+
     protected native void nativeStartVariationsSession(String restrictMode);
+    protected native String nativeGetLatestCountry();
 }