Fix Java Bridge wrapper properties cleanup for multi-frame pages

Java Bridge implementation was supposing to use a single JavaScript interface
object across different contexts (e.g. iframes).  But in fact, it is preferred
to have a JS interface wrapper per context, otherwise ads, for example, could
see the properties set on the wrapper by the main page.  The patch called
"Recycle old V8 wrapper objects on navigations" has already started fixing
this, but when cleaning up a wrapper for one frame it was invalidating a
backwards connection to NPObject from a wrapper living in another frame.

Bug: 15572824
Change-Id: Ia33845b45b50ff5bfcb88887c6a3f4f7c6c8703e
3 files changed