Issues with suspened and unsuspend caused by tab discarding

[deanoemcke]

Related to #901. Seems to only happen with certain chrome flags set, and after coming back to a session after a long period of time.

1. When unsuspending multiple tabs with 'unsuspend selected', if there are 3 or more tabs selected, then the middle tabs will not unsuspend even though they are specifically given a chrome.tabs.update(tabId, unsuspendedUrl) command.

2. Sometimes a tab that is suspending will be discarded before it finishes initialising the suspended state. This causes a bad favicon and title situation.

[deanoemcke]

Fix for 1. was to set tab property autoDiscardable to false when reloading. This seems to force the unsuspend. NOTE: The tabs autoDiscardable value is set back to true once the tab has finished unsuspending.

Fix for 2. was to trigger a tab init and check not only on the suspended tab status === complete event, but also on a discarded event.