Bug #15292, r=dp. Made the component manager inherit from |nsSupportsWeakReference|, fixed its |QueryInterface()| appropriately, and added casts in two places that became ambiguous now that the component manager had multiple |nsISupports| in it. Now one can hold a weak reference to the component manager using |nsIWeakReference|.

xpcom/build/nsXPComInit.cpp

@@ -206,7 +206,7 @@ nsresult NS_COM NS_InitXPCOM(nsIServiceManager* *result,
         nsComponentManagerImpl::gComponentManager = compMgr;
     }
     
-    rv = servMgr->RegisterService(kComponentManagerCID, compMgr);
+    rv = servMgr->RegisterService(kComponentManagerCID, NS_STATIC_CAST(nsIComponentManager*, compMgr));
     if (NS_FAILED(rv)) return rv;
 
     // 3. Register the global services with the component manager so that

xpcom/components/nsComponentManager.cpp

@@ -290,7 +290,7 @@ nsComponentManagerImpl::~nsComponentManagerImpl()
 
 }
 
-NS_IMPL_ISUPPORTS(nsComponentManagerImpl, NS_GET_IID(nsIComponentManager));
+NS_IMPL_ISUPPORTS2(nsComponentManagerImpl, nsIComponentManager, nsISupportsWeakReference)
 
 ////////////////////////////////////////////////////////////////////////////////
 // nsComponentManagerImpl: Platform methods

xpcom/components/nsComponentManager.h

@@ -28,6 +28,7 @@
 #include "prtime.h"
 #include "prmon.h"
 #include "nsCOMPtr.h"
+#include "nsWeakReference.h"
 
 class nsFactoryEntry;
 class nsDll;
@@ -44,7 +45,7 @@ extern const char XPCOM_LIB_PREFIX[];
 
 ////////////////////////////////////////////////////////////////////////////////
 
-class nsComponentManagerImpl : public nsIComponentManager {
+class nsComponentManagerImpl : public nsIComponentManager, public nsSupportsWeakReference {
 public:
     NS_DECL_ISUPPORTS
     NS_DECL_NSICOMPONENTMANAGER

xpcom/components/nsNativeComponentLoader.cpp

@@ -365,7 +365,7 @@ nsFreeLibrary(nsDll *dll, nsIServiceManager *serviceMgr, PRInt32 when)
     // Get the module object
     nsCOMPtr<nsIModule> mobj;
     /* XXXshaver cheat and use the global component manager */
-    rv = dll->GetModule(nsComponentManagerImpl::gComponentManager,
+    rv = dll->GetModule(NS_STATIC_CAST(nsIComponentManager*, nsComponentManagerImpl::gComponentManager),
                         getter_AddRefs(mobj));
     if (NS_SUCCEEDED(rv))
         {