[Webapp Refactor] Clean up remoting.Clipboard.
Currently, remoting.Clipboard is exposed as a global, such that it can hook
events across different files, e.g. remoting.js, client_plugin_impl.js, application.js
This CL moves clean up the file by:
1. Only create an instance of the clipboard when a session is connected. This removes
the startSession() method on the clipboard.
2. Hook all events (copy/paste/focus changes) from within remoting.clipboard, which
eliminates the need to have a global and effectively makes all its methods private.
3. Style cleanups, use single quotes for strings, make sure private variables are
post-fixed with underscores.
BUG=475317
Review URL: https://codereview.chromium.org/
1078563002
Cr-Commit-Position: refs/heads/master@{#324354}