Actually free plugin implement vars when running out of process when the

ppapi/shared_impl/var_tracker.h

 // Copyright (c) 2012 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.
 
 #ifndef PPAPI_SHARED_IMPL_VAR_TRACKER_H_
 #define PPAPI_SHARED_IMPL_VAR_TRACKER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/hash_tables.h"
 #include "base/memory/ref_counted.h"
 #include "base/threading/non_thread_safe.h"
+#include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_module.h"
 #include "ppapi/c/pp_var.h"
 #include "ppapi/shared_impl/ppapi_shared_export.h"
 
 namespace ppapi {
 
 class ArrayBufferVar;
 class Var;
 
 // Tracks non-POD (refcounted) var objects held by a plugin.
@@ skipping 53 matching lines @@
   // used in production code. The PP_Vars are returned in no particular order,
   // and their reference counts are unaffected.
   std::vector<PP_Var> GetLiveVars();
 
   // Retrieves the internal reference counts for testing. Returns 0 if we
   // know about the object but the corresponding value is 0, or -1 if the
   // given object ID isn't in our map.
   int GetRefCountForObject(const PP_Var& object);
   int GetTrackedWithNoReferenceCountForObject(const PP_Var& object);
 
+  // Called after an instance is deleted to do var cleanup.
+  virtual void DidDeleteInstance(PP_Instance instance) = 0;
+
  protected:
   struct VarInfo {
     VarInfo();
     VarInfo(Var* v, int input_ref_count);
 
     scoped_refptr<Var> var;
 
     // Explicit reference count. This value is affected by the renderer calling
     // AddRef and Release. A nonzero value here is represented by a single
     // reference in the host on our behalf (this reduces IPC traffic).
@@ skipping 64 matching lines @@
   // implemented by the Host and Plugin tracker separately, so that it can be
   // a real WebKit ArrayBuffer on the host side.
   virtual ArrayBufferVar* CreateArrayBuffer(uint32 size_in_bytes) = 0;
 
   DISALLOW_COPY_AND_ASSIGN(VarTracker);
 };
 
 }  // namespace ppapi
 
 #endif  // PPAPI_SHARED_IMPL_VAR_TRACKER_H_