Use explicit WebString conversions in plugins code

chrome/renderer/plugins/chrome_plugin_placeholder.cc

Index: chrome/renderer/plugins/chrome_plugin_placeholder.cc
diff --git a/chrome/renderer/plugins/chrome_plugin_placeholder.cc b/chrome/renderer/plugins/chrome_plugin_placeholder.cc
index 2c4677daea754c09448b1ae4f6325ce44a228832..c40e8e47dea5cee9aa67f0a231ab56c286af30b8 100644
--- a/chrome/renderer/plugins/chrome_plugin_placeholder.cc
+++ b/chrome/renderer/plugins/chrome_plugin_placeholder.cc
@@ -104,7 +104,7 @@ ChromePluginPlaceholder* ChromePluginPlaceholder::CreateLoadableMissingPlugin(
 
   // Will destroy itself when its WebViewPlugin is going away.
   return new ChromePluginPlaceholder(render_frame, frame, params, html_data,
-                                     params.mimeType);
+                                     params.mimeType.utf16());
 }
 
 // static