According to Twitter user IshanAgarwal24, Google Lens will work in the Camera app of the Pixel 3, mostly due to the improved NPU and the Hexagon 685 DSP that Qualcomm put in the Snapdragon 845 SoC.
The leak is part of a series of features that will come with the Pixel 3 devices. While some of them like Now Playing, Active Edge, Google Assistant are well-known and used by many Pixel owners, the Google Lens is something new.
Currently, the Google Lens feature is available in the Sandwich Menu in the upper left corner of the Camera application. It can be used after a picture is taken and is situated in the Photos menu of the Pixel phones.