[WebExtension port] move from nsIContentPolicy etc. to WebRequest etc.

[myrdd]

One important current question is: On a page load— when a new page is replaced by an old one —how to determine whether a request belongs to the new or the old page?
I'm probably going to use some uBO code here. uBO's implementation includes:

• PageRequestStore objects are used to store net requests
  • in RPC, this is the RequestMemory
• tabContextManager keeps track (as accurately as possible) of which root document belongs to which tab
  • tabContexts: Map<tabId, TabContext>
• connecting logic in … (reverse call tree)
  • bindTabToPageStats()
    • onHeadersReceived (traffic.js) — context="beforeRequest"
      • httpObserver.handleResponseHeaders (platform/firefox/vapi-background.js)
      • onHeadersReceived (platform/webext/vapi-webrequest.js)
    • onBeforeRootFrameRequest / onBeforeRequest (traffic.js) — context="beforeRequest"
      • httpObserver.handleRequest (platform/firefox/vapi-background.js)
      • onBeforeRequest (platform/webext/vapi-webrequest.js)
    • onUpdated (tab.js) — context="tabUpdated"
      • locationChangedListener (platform/firefox/vapi-background.js)
    • onNavigation (tab.js) — context="tabCommitted"
      • locationChangedListener (platform/firefox/vapi-background.js)
      • onBeforeRequest (traffic.js)
• µb tab.js
  • normalizeRequestDetails: essentially, set anyTabId, which is checked against only in onBeforeBehindTheSceneRequest (traffic.js)
• µb tab.js
  • updateBadgeAsync = updateBlockedContentStateAfterTimeout

These are the subtasks of this issue (incomplete)

• test TabContextManager
  • create/copy TabContext class
  • create/copy Context class
  • create "tabs.contexts" module
  • vAPI functions -> own functions
  • µb functions -> own functions
    • the functions
      • µb.normalizePageURL()
      • µb.URI.hostnameFromURI()
      • µb.URI.domainFromHostname()
    • create the TabContext properties
      • normalURL
      • rootHostname
      • rootDomain
    • , respectively.
    • which of those properties do we need on lookup() invocations?
  • call commit() and push()
    • uBO calls these functions in
      • onBeforeRootFrameRequest
      • onHeadersReceived
      • tabs.onUpdated
      • tabs.onNavigation
  • …
• …