Use an interface to get to the C++ object pointer instead of casting directly...

chrome_frame/bind_context_info.h

 // Copyright (c) 2010 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 CHROME_FRAME_BIND_CONTEXT_INFO_
 #define CHROME_FRAME_BIND_CONTEXT_INFO_
 
 #include <atlbase.h>
 #include <atlcom.h>
 
 #include "base/scoped_bstr_win.h"
 #include "base/scoped_comptr_win.h"
 
+class __declspec(uuid("71CC3EC7-7E8A-457f-93BC-1090CF31CC18"))
+IBindContextInfoInternal : public IUnknown {
+ public:
+  STDMETHOD(GetCppObject)(void** me) = 0;
+};
+
 // This class maintains contextual information used by ChromeFrame.
 // This information is maintained in the bind context.
-class BindContextInfo : public IUnknown, public CComObjectRoot {
+class BindContextInfo
+  : public IBindContextInfoInternal,
+    public CComObjectRoot {
  public:
   BindContextInfo();
-  virtual ~BindContextInfo() {}
+  ~BindContextInfo();
 
   BEGIN_COM_MAP(BindContextInfo)
-    COM_INTERFACE_ENTRY(IUnknown)
+    COM_INTERFACE_ENTRY(IBindContextInfoInternal)
+    COM_INTERFACE_ENTRY_AGGREGATE(IID_IMarshal, ftm_)
   END_COM_MAP()
 
   // Returns the BindContextInfo instance associated with the bind
   // context. Creates it if needed.
   static BindContextInfo* FromBindContext(IBindCtx* bind_context);
 
   void set_chrome_request(bool chrome_request) {
     chrome_request_ = chrome_request;
   }
 
@@ skipping 12 matching lines @@
   bool is_switching() const {
     return is_switching_;
   }
 
   void SetToSwitch(IStream* cache);
 
   IStream* cache() {
     return cache_;
   }
 
-  void set_url(const std::wstring& url) {
-    url_ = url;
+  // Accept a const wchar_t* to ensure that we don't have a reference
+  // to someone else's buffer.
+  void set_url(const wchar_t* url) {
+    DCHECK(url);
+    if (url) {
+      url_ = url;
+    } else {
+      url_.clear();
+    }
   }
 
-  const std::wstring url() const {
+  const std::wstring& url() const {
     return url_;
   }
 
  private:
+  STDMETHOD(GetCppObject)(void** me) {
+    DCHECK(me);
+    *me = static_cast<BindContextInfo*>(this);
+    return S_OK;
+  }
+
+ private:
   ScopedComPtr<IStream> cache_;
   bool no_cache_;
   bool chrome_request_;
   bool is_switching_;
   std::wstring url_;
+  ScopedComPtr<IUnknown> ftm_;
 
   DISALLOW_COPY_AND_ASSIGN(BindContextInfo);
 };
 
 #endif  // CHROME_FRAME_BIND_CONTEXT_INFO_