Revert 130199 - Revert 128179 - Make sure the plugin scriptable object is released before NPP_Destr…

Revert 130199 - Revert 128179 - Make sure the plugin scriptable object is released before NPP_Destroy.

We're reinstating this patch based on its impact on plugin crash rates between 20.0.1089.0 (with patch) and 20.0.1090.0 (without) builds.

When the we tear down a plugin instance the plugin process first invokes NPP_Destroy, and then tears down the IPC channel to the renderer, to give NPP_Destroy a chance to do last-minute scripting.  When the IPC channel for the last instance is torn down we also clean up the IPC channels and stubs for any plugin-side NPObjects that remain.

We suspect that some plugins implement the scriptable object as part of the plugin instance, rather than independently ref-counted, so that our releasing the object after NPP_Destroy actually triggers the plugin process to crash.

This CL tears down the stub for the plugin's scriptable object before we call NPP_Destroy.

BUG=101968, 119414
Original Review URL: http://codereview.chromium.org/9817023
Revert Review URL: https://chromiumcodereview.appspot.com/9959078

TBR=cpu@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=130698