An empty MIME type doesn't match any plugin, no matter what they may claim....

webkit/glue/webframeloaderclient_impl.cc

 // Copyright (c) 2006-2008 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 "config.h"
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
 
@@ skipping 1228 matching lines @@
   if (net::IsSupportedMimeType(
           webkit_glue::CStringToStdString(mime_type.latin1())))
     return true;
 
   // If Chrome is started with the --disable-plugins switch, pluginData is null.
   WebCore::PluginData* plugin_data = webframe_->frame()->page()->pluginData();
 
   // See if the type is handled by an installed plugin, if so, we can show it.
   // TODO(beng): (http://b/1085524) This is the place to stick a preference to
   //             disable full page plugins (optionally for certain types!)
-  return plugin_data && plugin_data->supportsMimeType(mime_type);
+  return !mime_type.isEmpty() && plugin_data && plugin_data->supportsMimeType(mime_type);
 }
 
 bool WebFrameLoaderClient::representationExistsForURLScheme(const String& URLScheme) const {
   // FIXME
   return false;
 }
 
 String WebFrameLoaderClient::generatedMIMETypeForURLScheme(const String& URLScheme) const {
   // This appears to generate MIME types for protocol handlers that are handled
   // internally. The only place I can find in the WebKit code that uses this
@@ skipping 273 matching lines @@
 
     if (mime_type.isEmpty())
       return ObjectContentFrame;
   }
 
   if (MIMETypeRegistry::isSupportedImageMIMEType(mime_type))
     return ObjectContentImage;
 
   // If Chrome is started with the --disable-plugins switch, pluginData is null.
   PluginData* plugin_data = webframe_->frame()->page()->pluginData();
-  if (plugin_data && plugin_data->supportsMimeType(mime_type))
+  if (!mime_type.isEmpty() && plugin_data && plugin_data->supportsMimeType(mime_type))

[jam, 2009/04/02 20:31:34]

I believe this one isn't needed because of line 1527

[Pam (message me for reviews), 2009/04/02 20:34:07]

Right. Removed.

     return ObjectContentNetscapePlugin;
 
   if (MIMETypeRegistry::isSupportedNonImageMIMEType(mime_type))
     return ObjectContentFrame;
 
   return ObjectContentNone;
 }
 
 String WebFrameLoaderClient::overrideMediaType() const {
   // FIXME
@@ skipping 28 matching lines @@
   if (!web_view) {
     return NULL;
   }
   WebDevToolsAgentImpl* tools_agent = web_view->GetWebDevToolsAgentImpl();
   if (tools_agent) {
     return tools_agent->net_agent_impl();
   } else {
     return NULL;
   }
 }