Timeline for loading a page:
Navigation start  ---> Pending navigation (with possible redirects) ---> Commit ---> Loading ----> Done

Notes from creis@:
The backwards spinner seemed to happen for part of the "pending navigation" phase but it converts to a forwards spinner well before commit.

Proposal:
From Navigation start --> Commit, we should show the connecting animation, rather than jumping forward to the loading animation before commit.

The new loading animation is determinate so should be shown when loading starts rather than the possibility of looking stuck at 0%. 

The offset of this might be that it might feel slower initially, but the loading phase should progress accurately. We'll need to monitor when this lands and if this changes the perceive load speed.