Try to show the printer management UI on Linux for unknown DEs.

In the current Linux ShowPrinterManagerDialog() implementation, if the
desktop environment is "OTHER" then an error log entry gets generated
and nothing else happens. To improve this, just treat it like GNOME and
try some commands that may launch the printer management UI.

BUG=869845

Change-Id: I92da6fd3edcc9ca51b9f2b494b9762d5935ba9cf
Reviewed-on: https://chromium-review.googlesource.com/1159475Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588934}

chrome/browser/printing/printer_manager_dialog_linux.cc

@@ -58,10 +58,6 @@ void DetectAndOpenPrinterConfigDialog() {
 
   bool opened = false;
   switch (base::nix::GetDesktopEnvironment(env.get())) {
-    case base::nix::DESKTOP_ENVIRONMENT_GNOME:
-      opened = OpenPrinterConfigDialog(kSystemConfigPrinterCommand) ||
-               OpenPrinterConfigDialog(kGnomeControlCenterPrintersCommand);
-      break;
     case base::nix::DESKTOP_ENVIRONMENT_KDE4:
       opened = OpenPrinterConfigDialog(kKde4KcmPrinterCommand) ||
                OpenPrinterConfigDialog(kSystemConfigPrinterCommand);
@@ -77,10 +73,11 @@ void DetectAndOpenPrinterConfigDialog() {
     case base::nix::DESKTOP_ENVIRONMENT_XFCE:
       opened = OpenPrinterConfigDialog(kSystemConfigPrinterCommand);
       break;
+    case base::nix::DESKTOP_ENVIRONMENT_GNOME:
     case base::nix::DESKTOP_ENVIRONMENT_OTHER:
-      LOG(ERROR)
-          << "Failed to detect the command to open printer config dialog";
-      return;
+      opened = OpenPrinterConfigDialog(kSystemConfigPrinterCommand) ||
+               OpenPrinterConfigDialog(kGnomeControlCenterPrintersCommand);
+      break;
   }
   LOG_IF(ERROR, !opened) << "Failed to open printer manager dialog ";
 }