1505818 - Make the page registration lazy in profiler

Status: NEW

(Core :: Gecko Profiler, defect, P2)

Description

[Nazım Can Altınova [:canova][:canaltinova on phabricator]]

We landed the patches on bug 1417976. We are currently registering the pages on profiler. But we can do better with that. We can make the page registration lazy in some way.  Once we add a marker that refers to a page(`docshellId` + `historyId` pair)  we can create the `PageInformation`. We should do something like that because currently we are missing a point. 

Since we remove the `PageInformation` when we navigate to other page, if the profiler is not active, we might miss some `PageInformation` that some markers refer to.
 
For example, steps to reproduce:
- Open a web page
- Click on a link
- Start the profiler
- Go back to previous page
At this point, we don’t have the information of the current page in `RegisteredPages` array. It’s because we don’t register again when we navigate with the back/forward buttons.
To fix this we should either add a check for back/forward buttons to registration code or make the registration lazy.