Add the JNI code in order to let Java use the InterestsFetcher.

chrome/android/java/src/org/chromium/chrome/browser/ntp/InterestsService.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.ntp;
+
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.chrome.browser.profiles.Profile;
+
+/**
+ * Retrieve the user's interests.
+ */
+public class InterestsService {
+    private long mNativeInterestsService;
+
+    /**
+     * A user's interest.
+     */
+    public static class Interest {
+        private String mName;
+        private String mImageUrl;
+        private double mRelevance;

[Bernhard Bauer, 2015/09/29 14:04:04]

Make these final?

[PEConn, 2015/10/07 13:55:21]

Done.

+
+        public Interest(String name, String imageUrl, double relevance) {
+            this.mName = name;
+            this.mImageUrl = imageUrl;
+            this.mRelevance = relevance;
+        }
+
+        public String getName() {
+            return mName;
+        }
+
+        public String getImageUrl() {
+            return mImageUrl;
+        }
+
+        public double getRelevance() {
+            return this.mRelevance;

[Bernhard Bauer, 2015/09/29 14:04:04]

You can remove the `this.`.

[PEConn, 2015/10/07 13:55:21]

Done.

+        }
+    }
+    /**
+     * Interface for receiving the interests of a user.
+     */
+    public interface GetInterestsCallback {
+        /**
+         * Callback method for fetching the interests of a user.
+         * In case of an error an empty array will be returned.

[Bernhard Bauer, 2015/09/29 14:04:04]

Generally, it's useful to be able to distinguish between an actual empty array
and an error condition. Would returning null work?

[PEConn, 2015/10/07 13:55:21]

Done.

+         *
+         * @param interests The array of interests.
+         */
+        @CalledByNative("GetInterestsCallback")
+        public void onInterestsAvailableCallback(Interest[] interests);
+    }
+
+    /**
+     * InterestsService constructor requires a valid user profile object.
+     *
+     * @param profile The profile for which to fetch the interests
+     */
+    public InterestsService(Profile profile) {
+        mNativeInterestsService = nativeInit(profile);
+    }
+
+    /**
+     * Cleans up the C++ side of this class. This instance must not be used after calling destroy().
+     */
+    public void destroy() {
+        assert mNativeInterestsService != 0;
+        nativeDestroy(mNativeInterestsService);
+        mNativeInterestsService = 0;
+    }
+
+    public void getInterests(final GetInterestsCallback callback) {
+        GetInterestsCallback wrappedCallback = new GetInterestsCallback() {
+            @Override
+            public void onInterestsAvailableCallback(Interest[] interests) {
+                // Don't notify callback if we've already been destroyed.

[Bernhard Bauer, 2015/09/29 14:04:04]

Is this actually going to be necessary? The native part uses weak pointers, so
we know that this callback will never be called when it's destroyed.

[PEConn, 2015/10/07 13:55:21]

Done.

+                if (mNativeInterestsService != 0) {
+                    callback.onInterestsAvailableCallback(interests);
+                }
+            }
+        };
+
+        nativeGetInterests(mNativeInterestsService, wrappedCallback);
+    }
+
+    /*
+     * Helper method for the native part.
+     */
+    @CalledByNative
+    public static Interest createInterest(String name, String imageUrl, double relevance) {

[Bernhard Bauer, 2015/09/29 14:04:04]

If this method is only meant to be called from native, you can make it private
(JNI don't care about that).

[PEConn, 2015/10/07 13:55:21]

Done.

+        return new Interest(name, imageUrl, relevance);
+    }
+
+    private native long nativeInit(Profile profile);
+    private native void nativeDestroy(long nativeInterestsService);
+    private native void nativeGetInterests(
+            long nativeInterestsService, GetInterestsCallback callback);
+}