Emit error if unknown switch is passed to mojo_shell

mojo/shell/desktop/mojo_main.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <algorithm>
 #include <iostream>
 
 #include "base/at_exit.h"
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 87 matching lines @@
 }
 
 }  // namespace
 
 int main(int argc, char** argv) {
   base::AtExitManager at_exit;
   base::CommandLine::Init(argc, argv);
 
   const base::CommandLine& command_line =
     *base::CommandLine::ForCurrentProcess();
-  if (!command_line.HasSwitch(switches::kEnableExternalApplications) &&
-      (command_line.HasSwitch(switches::kHelp) ||
-       command_line.GetArgs().empty())) {
+
+  const std::set<std::string> all_switches = switches::GetAllSwitches();
+  const base::CommandLine::SwitchMap switches = command_line.GetSwitches();
+  bool found_unknown_switch = false;
+  for (const auto& s : switches) {
+    if (all_switches.find(s.first) == all_switches.end()) {
+      std::cerr << "unknown switch: " << s.first << std::endl;
+      found_unknown_switch = true;
+    }
+  }
+
+  if (found_unknown_switch ||
+      (!command_line.HasSwitch(switches::kEnableExternalApplications) &&
+       (command_line.HasSwitch(switches::kHelp) ||
+        command_line.GetArgs().empty()))) {
     Usage();
     return 0;
   }
 
 #if defined(OS_LINUX)
   // We use gfx::RenderText from multiple threads concurrently and the pango
   // backend (currently the default on linux) is not close to threadsafe. Force
   // use of the harfbuzz backend for now.
   base::CommandLine::ForCurrentProcess()->AppendSwitch(
       kEnableHarfBuzzRenderText);
@@ skipping 24 matching lines @@
         if (IsArgsFor(argv[i], &args_for_value))
           GetAppURLAndSetArgs(args_for_value, &shell_context);
       }
 
       message_loop.PostTask(FROM_HERE, base::Bind(RunApps, &shell_context));
       message_loop.Run();
     }
   }
   return 0;
 }