Support navigations where triggered resource loads bypass the cache

[jgraham]

For WebDriver-BiDi we want a way to initiate a force reload (similar to shift-reload in some desktop browsers, or bypass cache in some devtools). This should cause fetches to happen in cache mode "reload" and bypass service-workers. Service worker itself seems to allow this possibility in a somewhat handwavy way (step 15.3 says "If request is a navigation request and the navigation triggering it was initiated with a shift+reload or equivalent, return null.").

In HTML the main problem is that subresource loads are mostly triggered implictly with each element containing a subresource having a list of conditions in which the load algorithm is triggered. This makes it hard to pass in parameters to the loading. Of course it's probably possible to replicate the same style (something like "if this algorithm was triggered by a navigation and the navigation params for that navigation has the force reload flag set, let request's cache mode be "reload"), but that doesn't seem very precise.

[annevk]

It seems to me that this is essentially a state of the client/environment/document that subresource fetches observe (and have access to) and adjust their policy on.

One thing I wondered about thinking through this is whether there's a lifetime aspect to this state or is the client/environment/document essentially considered reloaded in this manner forever, even if its days after the main load event fired.

cc @wanderview @jakearchibald

[jgraham]

Yeah, so I'm not sure if this ends up affecting all resource loads, or only those that are directly initiated by the navigation. And I'd kind of assumed that each resource is reloaded once and after that normal cache behaviour resumes, but maybe that's not true either.

[jakearchibald]

A quick test suggests that things fetched after window.onload will still go via the cache. I don't know where the 'cutoff point' is.

[domenic]

Related: #5222