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

chrome/browser/android/interests_service.cc

+// 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.
+
+#include "chrome/browser/android/interests_service.h"
+
+#include "base/android/jni_android.h"
+#include "base/android/jni_array.h"
+#include "base/android/jni_string.h"
+#include "base/android/scoped_java_ref.h"
+#include "chrome/browser/interests/interests_fetcher.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/profiles/profile_android.h"
+#include "jni/InterestsService_jni.h"
+
+using base::android::AttachCurrentThread;
+using base::android::ConvertJavaStringToUTF8;
+using base::android::ConvertUTF8ToJavaString;
+using base::android::ScopedJavaGlobalRef;
+using base::android::ScopedJavaLocalRef;
+using base::android::ToJavaArrayOfStrings;
+
+const char kInterestJavaClass[] =

[Bernhard Bauer, 2015/10/07 15:26:37]

This is now unused.

[PEConn, 2015/10/07 18:27:20]

Done.

+    "org/chromium/chrome/browser/ntp/InterestsService$Interest";
+
+InterestsService::InterestsService(Profile* profile)
+    : profile_(profile), weak_ptr_factory_(this) {}
+
+InterestsService::~InterestsService() {}
+
+void InterestsService::Destroy(JNIEnv* env, jobject obj) {
+  delete this;
+}
+
+void InterestsService::GetInterests(JNIEnv* env,
+                                    jobject obj,
+                                    jobject j_callback_obj) {
+
+  ScopedJavaGlobalRef<jobject> j_callback(env, j_callback_obj);
+
+  scoped_ptr<InterestsFetcher> fetcher =
+      InterestsFetcher::CreateFromProfile(profile_);
+
+  InterestsFetcher::InterestsCallback callback = base::Bind(
+      &InterestsService::OnObtainedInterests,
+      weak_ptr_factory_.GetWeakPtr(),
+      base::Owned(fetcher.get()),

[Marc Treib, 2015/10/07 15:03:01]

Can you use base::Passed(fetcher), and remove the ugly explicit release() below?
(Get a raw pointer to fetcher first, and call FetchInterests using that.) As it
is, fetcher has two owners for a brief period.

[PEConn, 2015/10/07 18:27:20]

Done.

+      j_callback);
+
+  fetcher->FetchInterests(callback);
+
+  // The callback owns InterestsFetcher now.
+  ignore_result(fetcher.release());
+}
+
+// static
+bool InterestsService::Register(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+jobjectArray InterestsService::ConvertInterestsToJava(
+    scoped_ptr<std::vector<InterestsFetcher::Interest>> interests) {
+  if (!interests)
+    return nullptr;
+
+  JNIEnv* env = AttachCurrentThread();

[Bernhard Bauer, 2015/10/07 15:26:37]

What I meant in my previous comment was to pass |env| as a parameter into this
method. That does not require you to wrap it in a callback.

[PEConn, 2015/10/07 18:27:20]

Done.

+
+  jobjectArray j_interests =
+      Java_InterestsService_createInterestsArray(env, interests->size()).obj();
+
+  for (size_t i = 0; i != interests->size(); i++) {
+    auto& interest = interests->at(i);

[Bernhard Bauer, 2015/10/07 15:26:37]

Isn't this type just InterestsFetcher::Interest? I don't think using auto makes
things clearer here.

Also, use the [] operator instead of `at` (you might have to do it like this:
(*interests)[i]), as the latter throws an exception, but we don't use exceptions
in C++.

Oh hey, couldn't you just use a C++11-style for-loop? (But please still with an
explicit type.)

[PEConn, 2015/10/07 18:27:20]

Done. Good point about at throwing an exception. I didn't want to change this to
a for-each since we need the index (to insert into the java array at the correct
point).

+    ScopedJavaLocalRef<jobject> j_interest =
+        Java_InterestsService_createInterest(
+            env,
+            ConvertUTF8ToJavaString(env, interest.name).obj(),
+            ConvertUTF8ToJavaString(env, interest.image_url.spec()).obj(),
+            interest.relevance);
+
+    env->SetObjectArrayElement(j_interests, i, j_interest.obj());
+  }
+
+  return j_interests;
+}
+
+void InterestsService::OnObtainedInterests(
+    InterestsFetcher* fetcher,
+    const ScopedJavaGlobalRef<jobject>& j_callback,
+    scoped_ptr<std::vector<InterestsFetcher::Interest>> interests) {
+

[Marc Treib, 2015/10/07 15:03:01]

nit: remove empty line

[PEConn, 2015/10/07 18:27:20]

Done.

+  JNIEnv* env = AttachCurrentThread();
+  jobjectArray j_interests = ConvertInterestsToJava(interests.Pass());
+  Java_GetInterestsCallback_onInterestsAvailableCallback(env,
+                                                         j_callback.obj(),
+                                                         j_interests);
+}
+
+static jlong Init(JNIEnv* env,
+                  const JavaParamRef<jobject>& jobj,
+                  const JavaParamRef<jobject>& jprofile) {
+  InterestsService* interests_service =
+      new InterestsService(ProfileAndroid::FromProfileAndroid(jprofile));
+  return reinterpret_cast<intptr_t>(interests_service);
+}