Re-land http://codereview.chromium.org/211031 with a bug opened...

webkit/default_plugin/default_plugin_shared.h

Index: webkit/default_plugin/default_plugin_shared.h
===================================================================
--- webkit/default_plugin/default_plugin_shared.h	(revision 28818)
+++ webkit/default_plugin/default_plugin_shared.h	(working copy)
@@ -11,11 +11,11 @@
 namespace default_plugin {
 
 // We use the NPNGetValue host function to send notification message to host.
-// This corresponds to NPNVariable defined in npapi.h. However, we don't care
-// too much about value conflicts because on the host side, it will only respond
-// to such request coming from default plugin.
-const int kMissingPluginStatusStart = 3000;
+// This corresponds to NPNVariable defined in npapi.h, and should be chosen so
+// as to not overlap values if NPAPI is updated.
 
+const int kMissingPluginStatusStart = 5000;
+
 enum MissingPluginStatus {
   MISSING_PLUGIN_AVAILABLE,
   MISSING_PLUGIN_USER_STARTED_DOWNLOAD