The sandbox blocks GetTempFileName's prior response, causing the system to end up searching a number of (inaccessible) folders to use as a replacement for the temp folder.  This patch provides a path to a new folder on the command line for the plugin process.  This new temp folder, specific to this plugin process instance, is then communicated to the system via the TEMP/TMP environment variables.  This is similar to what is done for the content process but avoids nsDirectoryService, which doesn't exist in plugin processes.

Differential Revision: https://phabricator.services.mozilla.com/D7532

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extra : moz-landing-system : lando