Tabs are not loading discarded, even when requested to

[petemill]

Description

#12916 was mitigating a bug with discarding tabs (automatically) which had already been loaded, and causing them to not be able to be switched to (#10673).

However, it also unintentionally results in startup tabs not being created 'unloaded' (or 'discarded'), meaning they all load simultaneously. This does not need to be the case as tabs during startup are not affected by #10673.

Steps to Reproduce

Cases 1:

1. Create many tabs (regular http / https sites)
2. Quit Brave
3. Load Brave again and ensure that only the active tab is loaded (others should be lazy loaded)

Cases 2:

1. Set up a profile on 0.19.147 with 4 windows and multiple tabs (approximately 160-180 tabs between the 4 windows)
2. Launched Brave using 0.20.29
3. Experienced all tabs trying to load at once.
4. Waited for them all to load. Once they load, click on a tab and verify that it was loaded
5. Closed 0.20.29 and launched 0.20.30.
6. Not all tabs tried to load at once . Clicking/Hovering over a lazy loaded tab should load the tab

Actual result:
Tabs are all loaded

Expected result:
Only active tab is loaded

Reproduces how often:
100%

Brave Version

about:brave info:
0.20

[esmail]

Thanks for fixing. Just want to point out that this was especially painful for us tab hoarders, since #2702 meant that any tabs that didn't end up loading successfully were effectively lost for good after quitting.