Deal with preloadded pages in Safari 7.0

Safari 7.0 runs content scripts in preloaded pages. However our high-level code expects only the page that the user can see, to be running in a tab. So we have to defer all requests from preloaded pages to the background page until the page is shown.

[Wladimir Palant, 2014-01-24 14:11:34]

I didn't finish this review, IMHO we are trying to save a leaky abstraction
here. Discussing this in chat now.

http://codereview.adblockplus.org/5092502491103232/diff/5629499534213120/safa...
File safari/ext/background.js (right):

http://codereview.adblockplus.org/5092502491103232/diff/5629499534213120/safa...
safari/ext/background.js:61: // when the "loading" message was sent form a
preloaded
form => from

http://codereview.adblockplus.org/5092502491103232/diff/5629499534213120/safa...
safari/ext/background.js:80: this._preloadedTabs.delete(tab);
What if a preloaded page is simply discarded? Won't we leak memory then?

[Sebastian Noack, 2014-01-24 14:17:49]

http://codereview.adblockplus.org/5092502491103232/diff/5629499534213120/safa...
File safari/ext/background.js (right):

http://codereview.adblockplus.org/5092502491103232/diff/5629499534213120/safa...
safari/ext/background.js:80: this._preloadedTabs.delete(tab);
On 2014/01/24 14:11:34, Wladimir Palant wrote:
> What if a preloaded page is simply discarded? Won't we leak memory then?

Just temporarily until another page is loaded in that tab. If that isn't enough
we could still make the TabMap remove data when the "unload" event was received
by the content script.

[Sebastian Noack, 2014-02-24 12:49:36]

This patch became obsolete in favor of
http://codereview.adblockplus.org/5464830253203456/