 PPB_URLLoader_Impl::~PPB_URLLoader_Impl() {
  // There is a path whereby the destructor for the loader_ member can
  // invoke InstanceWasDeleted() upon this PPB_URLLoader_Impl, thereby
  // re-entering the scoped_ptr destructor with the same scoped_ptr object
  // via loader_.reset(). Be sure that loader_ is first NULL then destroy
  // the scoped_ptr. See http://crbug.com/159429.
  scoped_ptr<WebKit::WebURLLoader> for_destruction_only(loader_.release());
 }

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.