message: Add some documentation of object lifetimes for the StatefulNnApiDelegate
  constructors and GetOptions method.
diff: @@ -130,16 +130,32 @@ class StatefulNnApiDelegate : public TfLiteDelegate {
  // Uses default options.
  StatefulNnApiDelegate();
  + // The ownership of the NnApi instance is left to the caller of the
  + // StatefulNnApiDelegate constructor; the caller must ensure that the lifetime
  + // of the NnApi instance exceeds the lifetime of the StatefulNnApiDelegate.
  explicit StatefulNnApiDelegate(const NnApi* nnapi);
  // The constructor that accepts options from user.
  + // This makes a copy of any data that it needs from Options, so
  + // the caller can safely deallocate any storage pointed to by
  + // the 'const char *' members of Options immediately after calling this.
  explicit StatefulNnApiDelegate(Options options);
  + // Constructor that accepts both an NnApi instance and options.
  + // The ownership of the NnApi instance is left to the caller of the
  + // StatefulNnApiDelegate constructor; the caller must ensure that the lifetime
  + // of the NnApi instance exceeds the lifetime of the StatefulNnApiDelegate.
  + // This constructor makes a copy of any data that it needs from Options, so
  + // the caller can safely deallocate any storage pointed to by
  + // the 'const char *' members of Options immediately after calling this.
  StatefulNnApiDelegate(const NnApi* nnapi, Options options);
  ~StatefulNnApiDelegate() = default;
  // Returns the delegate options.
  + // The lifetime of the storage pointed to by the 'const char *' members of the
  + // returned Options object is the same as the lifetime of the supplied
  + // TfLiteDelegate instance.
  static const Options GetOptions(TfLiteDelegate* delegate);
  // Callback function which copies data from ANeuralNetworksMemory to host
  