Avoid Android modifications to JavaNPObjectV8.cpp/h

Avoid Android modifications to JavaNPObjectV8.cpp/h

https://android-git.corp.google.com/g/40387 fixed a long-standing bug to
avoid leaking references to injected Java objects. However, it did so by
making changes to JavaNPObjectV8.cpp/h which were never upstreamed. This
change avoids the need for these changes.

This change also avoids the use of a local PassRefPtr, which was
incorrectly introduced in https://android-git.corp.google.com/g/36204.

Change-Id: I6b17e85f7991e5226e00e7b041c38e2ca3d0cf57