[android] self-contained map renderer

- Isolates the GL thread in a MapRenderer class with a native peer

platform/android/src/map_renderer_runnable.cpp

@@ -0,0 +1,49 @@
+#include "map_renderer_runnable.hpp"
+
+#include <mbgl/util/logging.hpp>
+
+namespace mbgl {
+namespace android {
+
+MapRendererRunnable::MapRendererRunnable(jni::JNIEnv& env, std::weak_ptr<Mailbox> mailbox_)
+    : mailbox(std::move(mailbox_)) {
+
+    // Create the Java peer
+    jni::UniqueLocalFrame frame = jni::PushLocalFrame(env, 5);
+    static auto constructor = javaClass.GetConstructor<jlong>(env);
+    auto instance = javaClass.New(env, constructor, reinterpret_cast<jlong>(this));
+    javaPeer = SeizeGenericWeakRef(env, jni::Object<MapRendererRunnable>(jni::NewWeakGlobalRef(env, instance.Get()).release()));
+}
+
+MapRendererRunnable::~MapRendererRunnable() = default;
+
+void MapRendererRunnable::run(jni::JNIEnv&) {
+    Mailbox::maybeReceive(mailbox);
+}
+
+jni::Object<MapRendererRunnable> MapRendererRunnable::getPeer() {
+    return *javaPeer;
+}
+
+// Static methods //
+
+jni::Class<MapRendererRunnable> MapRendererRunnable::javaClass;
+
+void MapRendererRunnable::registerNative(jni::JNIEnv& env) {
+    // Lookup the class
+    MapRendererRunnable::javaClass = *jni::Class<MapRendererRunnable>::Find(env).NewGlobalRef(env).release();
+
+#define METHOD(MethodPtr, name) jni::MakeNativePeerMethod<decltype(MethodPtr), (MethodPtr)>(name)
+
+    jni::RegisterNativePeer<MapRendererRunnable>(
+            env,
+            MapRendererRunnable::javaClass,
+            "nativePtr",
+            std::make_unique<MapRendererRunnable, JNIEnv&>,
+            "nativeInitialize",
+            "finalize",
+            METHOD(&MapRendererRunnable::run, "run"));
+}
+
+} // namespace android
+} // namespace mbgl