Use a placeholder instead of the default plugin for missing plug-ins on Mac and Linux.

chrome/common/default_plugin.cc

 // Copyright (c) 2010 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 "chrome/common/default_plugin.h"
 
 #include "chrome/default_plugin/plugin_main.h"
 #include "webkit/plugins/npapi/plugin_list.h"
 
 namespace chrome {
 
 void RegisterInternalDefaultPlugin() {
+#if defined(OS_WIN)
+  // TODO(bauerb): On Windows the default plug-in can download and install
+  // missing plug-ins, which we don't support in the browser yet, so keep
+  // using the default plug-in on Windows until we do.
   const webkit::npapi::PluginEntryPoints entry_points = {
 #if !defined(OS_POSIX) || defined(OS_MACOSX)
     default_plugin::NP_GetEntryPoints,
 #endif
     default_plugin::NP_Initialize,
     default_plugin::NP_Shutdown
   };
 
   webkit::npapi::PluginList::Singleton()->RegisterInternalPlugin(
       FilePath(webkit::npapi::kDefaultPluginLibraryName),
       "Default Plug-in",
       "Provides functionality for installing third-party plug-ins",
       "*",
       entry_points);
+#endif  // defined OS(WIN)
 }
 
 }  // namespace chrome