Prevent reentrant destructors in the PluginModule.

webkit/plugins/ppapi/plugin_module.h

Index: webkit/plugins/ppapi/plugin_module.h
===================================================================
--- webkit/plugins/ppapi/plugin_module.h	(revision 104693)
+++ webkit/plugins/ppapi/plugin_module.h	(working copy)
@@ -138,6 +138,7 @@
   // release relevant resources and update all affected instances.
   void PluginCrashed();
 
+  bool is_in_destructor() const { return is_in_destructor_; }
   bool is_crashed() const { return is_crashed_; }
 
   // Reserves the given instance is unique within the plugin, checking for
@@ -173,6 +174,10 @@
 
   PP_Module pp_module_;
 
+  // True when we're running in the destructor. This allows us to write some
+  // assertions.
+  bool is_in_destructor_;
+
   // True if the plugin is running out-of-process and has crashed.
   bool is_crashed_;