Bug 1885893 - Only collect HTTPS-First telemetry on successful request r=freddyb

This patch addresses the problem that we currently collect HTTPS-First telemetry
for sites that are not reachable at all, be it through always causing a error or
through always timing out.

- On a downgrade, do not collect telemetry instantly, but instead save the
  telemetry data in the load state for the downgraded request
- That telemetry data will then be copied over into the document load listener
  of the new request
- On a successful request, if we have downgrade data in the load listener, we
  collect the downgrade telemetry, as the downgrade seems to have been
  successful
- Similar to the downgrade case, we only count the upgrade metric once we
  encounter a successful request annotated with the information that it was
  upgraded by HTTPS-First, instead of counting it instantly on the decision to
  upgrade. This also means the upgrade metric will not include loads that are
  downgraded again anymore
- Add a testcase for a site which is neither reachable via HTTP nor HTTPS, and
  ensure no telemetry is collected

Differential Revision: https://phabricator.services.mozilla.com/D210792

docshell/base/nsDocShellLoadState.h

@@ -24,6 +24,7 @@ class nsIURI;
 class nsIDocShell;
 class nsIChannel;
 class nsIReferrerInfo;
+struct HTTPSFirstDowngradeData;
 namespace mozilla {
 class OriginAttributes;
 template <typename, class>
@@ -148,6 +149,11 @@ class nsDocShellLoadState final {
 
   void SetIsExemptFromHTTPSFirstMode(bool aIsExemptFromHTTPSFirstMode);
 
+  RefPtr<HTTPSFirstDowngradeData> GetHttpsFirstDowngradeData() const;
+
+  void SetHttpsFirstDowngradeData(
+      RefPtr<HTTPSFirstDowngradeData> const& aHttpsFirstTelemetryData);
+
   bool OriginalFrameSrc() const;
 
   void SetOriginalFrameSrc(bool aOriginalFrameSrc);
@@ -484,6 +490,10 @@ class nsDocShellLoadState final {
   // will be exempt from HTTPS-Only-Mode upgrades.
   bool mIsExemptFromHTTPSFirstMode;
 
+  // If set, this load is a HTTPS-First downgrade, and the downgrade data will
+  // be submitted to telemetry later if the load succeeds.
+  RefPtr<HTTPSFirstDowngradeData> mHttpsFirstDowngradeData;
+
   // If this attribute is true, this load corresponds to a frame
   // element loading its original src (or srcdoc) attribute.
   bool mOriginalFrameSrc;