Add support for .so files in generate_gradle.py.

build/android/gradle/build.gradle.jinja

Index: build/android/gradle/build.gradle.jinja
diff --git a/build/android/gradle/build.gradle.jinja b/build/android/gradle/build.gradle.jinja
index 008a1d94f32c14486c2ac97940e27bad9d105b44..1475cea39ee026926fff0915aec2d8ceca608493 100644
--- a/build/android/gradle/build.gradle.jinja
+++ b/build/android/gradle/build.gradle.jinja
@@ -74,16 +74,17 @@ android {
 
         main.manifest.srcFile "{{ android_manifest }}"
 
-{% if template_type == 'android_library' %}
-        main {
-{% else %}
-        test {
-{% endif %}
+        {{ sourceSetName }} {
             java.srcDirs = [
 {% for path in java_dirs %}
                 "{{ path }}",
 {% endfor %}
             ]
+            jniLibs.srcDirs = [
+{% for path in jni_libs %}
+                "{{ path }}",
+{% endfor %}
+            ]
         }
     }
 }