Add some instrumentation to catch the source of a potential double-free.

content/plugin/npobject_stub.h

Index: content/plugin/npobject_stub.h
===================================================================
--- content/plugin/npobject_stub.h	(revision 98369)
+++ content/plugin/npobject_stub.h	(working copy)
@@ -11,6 +11,7 @@
 
 #include <vector>
 
+#include "base/debug/stack_trace.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "content/plugin/npobject_base.h"
@@ -85,6 +86,24 @@
                   IPC::Message* reply_msg);
 
  private:
+  //----------------------------------------------------------------------------
+  // Temporary code for debugging 94179
+  // TODO(eroman): Delete this when done investigating.
+  //----------------------------------------------------------------------------
+  void CheckIsAlive();
+  static void DeleteSoonHelper(
+      const base::debug::StackTrace& task_origin_stack_trace,
+      NPObjectStub* stub);
+
+  bool has_deletion_stack_trace_;
+  base::debug::StackTrace deletion_stack_trace_;
+
+  // Value to indicate whether this instance is alive or dead.
+  static const int kTokenAlive = 0x1Cd9fe38;
+  static const int kTokenDead = 0xDEADBEEF;
+  int liveness_token_;
+  //----------------------------------------------------------------------------
+
   NPObject* npobject_;
   scoped_refptr<PluginChannelBase> channel_;
   int route_id_;