Let WeakPtrFactory operations fail once its dtor is called

base/memory/weak_ptr.h

Index: base/memory/weak_ptr.h
diff --git a/base/memory/weak_ptr.h b/base/memory/weak_ptr.h
index b66f02431aac2aa48bcf9babc396de3d8e055095..cd7c176650ce748b0c48a0d34fbefd49b63ecd1c 100644
--- a/base/memory/weak_ptr.h
+++ b/base/memory/weak_ptr.h
@@ -232,22 +232,30 @@ class WeakPtrFactory {
   explicit WeakPtrFactory(T* ptr) : ptr_(ptr) {
   }
 
+  ~WeakPtrFactory() {
+    ptr_ = NULL;
+  }
+
   WeakPtr<T> GetWeakPtr() {
+    DCHECK(ptr_);
     return WeakPtr<T>(weak_reference_owner_.GetRef(), ptr_);
   }
 
   // Call this method to invalidate all existing weak pointers.
   void InvalidateWeakPtrs() {
+    DCHECK(ptr_);
     weak_reference_owner_.Invalidate();
   }
 
   // Call this method to determine if any weak pointers exist.
   bool HasWeakPtrs() const {
+    DCHECK(ptr_);
     return weak_reference_owner_.HasRefs();
   }
 
   // Indicates that this object will be used on another thread from now on.
   void DetachFromThread() {
+    DCHECK(ptr_);
     weak_reference_owner_.DetachFromThread();
   }