Register the worker process ID of the extension to ProcessMap in ExtensionSystem.

This change makes importScripts() work correctly in the Shared Worker of packaged app.

BUG=258695,329786

Review URL: https://codereview.chromium.org/139163002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247513 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247513