Add assetRoot for Android

gyp/platform-android.gypi

@@ -11,6 +11,7 @@
 
       'sources': [
         '../platform/android/log_android.cpp',
+        '../platform/android/asset_root.cpp',
         '../platform/default/string_stdlib.cpp',
         '../platform/default/image.cpp',
         '../platform/default/image_reader.cpp',

platform/android/asset_root.cpp

@@ -0,0 +1,16 @@
+#include <mbgl/platform/platform.hpp>
+#include <mbgl/android/jni.hpp>
+
+#include <uv.h>
+#include <libgen.h>
+
+namespace mbgl {
+namespace platform {
+
+// Returns the path to the root folder of the application.
+const std::string &assetRoot() {
+    return mbgl::android::apkPath;
+}
+
+}
+}