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

content/common/webkit_param_traits.h

Index: content/common/webkit_param_traits.h
diff --git a/content/common/webkit_param_traits.h b/content/common/webkit_param_traits.h
index 8fce34e1250d823c4282669bf28e6a0b8dcaf7ca..e6f8ed4dc62ea11bc33d5288e6aacf9a2c9e8696 100644
--- a/content/common/webkit_param_traits.h
+++ b/content/common/webkit_param_traits.h
@@ -26,6 +26,7 @@
 #include "webkit/glue/resource_type.h"
 #include "webkit/glue/webcursor.h"
 #include "webkit/glue/window_open_disposition.h"
+#include "webkit/plugins/webplugininfo.h"
 
 namespace webkit_glue {
 struct PasswordForm;
@@ -113,6 +114,22 @@ struct ParamTraits<NPIdentifier_Param> {
 };
 
 template <>
+struct ParamTraits<webkit::WebPluginMimeType> {
+  typedef webkit::WebPluginMimeType param_type;
+  static void Write(Message* m, const param_type& p);
+  static bool Read(const Message* m, void** iter, param_type* r);
+  static void Log(const param_type& p, std::string* l);
+};
+
+template <>
+struct ParamTraits<webkit::WebPluginInfo> {
+  typedef webkit::WebPluginInfo param_type;
+  static void Write(Message* m, const param_type& p);
+  static bool Read(const Message* m, void** iter, param_type* r);
+  static void Log(const param_type& p, std::string* l);
+};
+
+template <>
 struct ParamTraits<WebCursor> {
   typedef WebCursor param_type;
   static void Write(Message* m, const param_type& p) {