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::ScopedJavaGlobalRef;
+using base::android::ScopedJavaLocalRef;
+using base::android::ToJavaArrayOfStrings;
+
+namespace {
+
+const char kInterestJavaClass[] =

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

Const variables actually get internal linkage automatically, so the anonymous
namespace isn't really necessary if there is nothing else in there.

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

Done.

+    "org/chromium/chrome/browser/ntp/InterestsService$Interest";
+
+}  // end namespace

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

If you do keep the namespace, remove the "end ".

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

Done.

+
+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) {
+  scoped_ptr<ScopedJavaGlobalRef<jobject>> j_callback(

[Bernhard Bauer, 2015/09/29 14:04:05]

You don't actually need a scoped_ptr for a ScopedJavaGlobalRef: It's totally
fine to copy it around.

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

Done.

+      new ScopedJavaGlobalRef<jobject>());
+
+  j_callback->Reset(env, j_callback_obj);
+
+  InterestsFetcher* fetcher =

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

I would make this a scoped_ptr and only release() it below, so it's clearer
you're not leaking the pointer.

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

Done.

+      InterestsFetcher::CreateFromProfile(profile_).release();
+
+  InterestsFetcher::InterestsCallback callback = base::Bind(
+      &InterestsService::OnObtainedInterests, weak_ptr_factory_.GetWeakPtr(),
+      base::Owned(fetcher), base::Passed(&j_callback));
+
+  fetcher->Start(callback);
+}
+
+// static
+bool InterestsService::Register(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+jobjectArray InterestsService::ConvertInterestsToJava(
+    const std::vector<InterestsFetcher::Interest>& interests) {
+  JNIEnv* env = AttachCurrentThread();
+  jclass interest_class = env->FindClass(kInterestJavaClass);

[Bernhard Bauer, 2015/09/29 14:04:05]

It's not great to have to manually resolve this class (for example, it makes it
difficult to find references to the class when renaming it) -- Could you maybe
add a static Java method that will do this instead?

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

Done.

+
+  jobjectArray j_interests =
+      env->NewObjectArray(interests.size(), interest_class, 0);

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

I would use nullptr rather than 0.

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

Done.

+
+  for (size_t i = 0; i != interests.size(); i++) {
+    ScopedJavaLocalRef<jobject> j_interest =
+        Java_InterestsService_createInterest(
+            env, env->NewStringUTF(interests[i].name.c_str()),

[Bernhard Bauer, 2015/09/29 14:04:05]

Please use base::android::ConvertUTF8ToJavaString() rather than doing your own
thing.

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

Done.

+            env->NewStringUTF(interests[i].image_url.c_str()),
+            interests[i].relevance);
+
+    env->SetObjectArrayElement(j_interests, i, j_interest.obj());
+  }
+
+  return j_interests;
+}
+
+void InterestsService::OnObtainedInterests(
+    InterestsFetcher* fetcher,
+    scoped_ptr<ScopedJavaGlobalRef<jobject>> j_callback,
+    const std::vector<InterestsFetcher::Interest>& interests) {
+  JNIEnv* env = AttachCurrentThread();
+
+  jobjectArray j_interests =
+      InterestsService::ConvertInterestsToJava(interests);

[Bernhard Bauer, 2015/09/29 14:04:05]

You could pass the JNIEnv to this method. Also, you are already inside the
InterestsService class, so you don't need the InterestsService:: prefix.

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

Not Done. This would require passing the JNIEnv through a callback.

+
+  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));

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

The current version of the CL that this is based on has a static Create() method
that takes a Profile*.

+  return reinterpret_cast<intptr_t>(interests_service);
+}