Bug 1611472 - Add missing error codes r=mayhemer

In bug 1579049, response code 403 and 501 were changed to map to `NS_ERROR_PROXY_FORBIDDEN` and `NS_ERROR_PROXY_NOT_IMPLEMENTED`. This caused a regression, since 403 and 501 were mapping to `NS_ERROR_PROXY_CONNECTION_REFUSED` before. This patch fixes the regression by adding `NS_ERROR_PROXY_FORBIDDEN` and `NS_ERROR_PROXY_NOT_IMPLEMENTED` to nsDocShell.

Differential Revision: https://phabricator.services.mozilla.com/D61682

--HG--
extra : moz-landing-system : lando

docshell/base/nsDocShell.cpp

@@ -3852,6 +3852,8 @@ nsDocShell::DisplayLoadError(nsresult aError, nsIURI* aURI,
         error = "proxyResolveFailure";
         break;
       case NS_ERROR_PROXY_CONNECTION_REFUSED:
+      case NS_ERROR_PROXY_FORBIDDEN:
+      case NS_ERROR_PROXY_NOT_IMPLEMENTED:
       case NS_ERROR_PROXY_AUTHENTICATION_FAILED:
       case NS_ERROR_PROXY_TOO_MANY_REQUESTS:
         // Proxy connection was refused.
@@ -6364,6 +6366,8 @@ nsresult nsDocShell::EndPageLoad(nsIWebProgress* aProgress,
          aStatus == NS_ERROR_CONNECTION_REFUSED ||
          aStatus == NS_ERROR_UNKNOWN_PROXY_HOST ||
          aStatus == NS_ERROR_PROXY_CONNECTION_REFUSED ||
+         aStatus == NS_ERROR_PROXY_FORBIDDEN ||
+         aStatus == NS_ERROR_PROXY_NOT_IMPLEMENTED ||
          aStatus == NS_ERROR_PROXY_AUTHENTICATION_FAILED ||
          aStatus == NS_ERROR_PROXY_TOO_MANY_REQUESTS ||
          aStatus == NS_ERROR_MALFORMED_URI ||