Bug 1186467 - Rewrite NativeJSContainer to use new native JNI scheme; r=snorp

This patch makes NativeJSContainer use per-instance native methods.
NativeJSContainer is also updated to use smart JNI reference classes.

widget/android/AndroidBridge.cpp

@@ -1066,9 +1066,7 @@ AndroidBridge::HandleGeckoMessage(JSContext* cx, JS::HandleObject object)
 {
     ALOG_BRIDGE("%s", __PRETTY_FUNCTION__);
 
-    JNIEnv* const env = GetJNIEnv();
-    auto message = Object::LocalRef::Adopt(env,
-        mozilla::widget::CreateNativeJSContainer(env, cx, object));
+    auto message = mozilla::widget::CreateNativeJSContainer(cx, object);
     GeckoAppShell::HandleGeckoMessageWrapper(message);
 }