Bug 1900225: Part 4 - Add geo.prompt.open_system_prefs to block opening system preferences r=gstoll a=RyanVM

Also adds this as the default for mochitests, in anticipation of the day that
the implementation is supported by the computers in automation.

Differential Revision: https://phabricator.services.mozilla.com/D216475

dom/geolocation/Geolocation.cpp

@@ -1446,7 +1446,14 @@ void Geolocation::NotifyAllowedRequest(nsGeolocationRequest* aRequest) {
 
 /* static */ geolocation::SystemGeolocationPermissionBehavior
 Geolocation::GetLocationOSPermission() {
-  return geolocation::GetGeolocationPermissionBehavior();
+  auto permission = geolocation::GetGeolocationPermissionBehavior();
+
+  if (!StaticPrefs::geo_prompt_open_system_prefs() &&
+      permission == geolocation::SystemGeolocationPermissionBehavior::
+                        GeckoWillPromptUser) {
+    return geolocation::SystemGeolocationPermissionBehavior::NoPrompt;
+  }
+  return permission;
 }
 
 void Geolocation::RequestIfPermitted(nsGeolocationRequest* request) {

modules/libpref/init/StaticPrefList.yaml

@@ -5648,6 +5648,13 @@
   mirror: always
 #endif
 
+# If true, open system preferences for the user when geolocation is requested
+# by the user but OS geolocation permission is not available.
+- name: geo.prompt.open_system_prefs
+  type: bool
+  value: true
+  mirror: always
+
 #---------------------------------------------------------------------------
 # Prefs starting with "gfx."
 #---------------------------------------------------------------------------

testing/profiles/mochitest/user.js

@@ -31,3 +31,8 @@ user_pref("app.update.disabledForTesting", true);
 // Therefore, in the mochitest, as the frequently in common browser tests can be
 // super higher than the real user, we disable this feature.
 user_pref("places.history.floodingPrevention.enabled", false);
+
+// If we are on a platform where we can detect that we don't have OS geolocation
+// permission, and we can open it and wait for the user to give permission, then
+// don't do that.
+user_pref("geo.prompt.open_system_prefs", false);