Improved support for photo cropping is coming to the Chrome OS Gallery and Image Editor in the near future.
Free-form cropping of images is already supported in the Chrome image viewer but, right now, it’s not currently possible to select a predefined ratio (e.g., 1:1, 4:3, etc.) or constrain the proportions of a free-form crop.
Users coming from other apps on other operating systems often expect to be able to constrain the proportions of a crop rectangle when holding down a modifier key, such as Shift. It’s a feature of many photo editing applications, including Photoshop, Pixelmator and GIMP. Maintaining consistency in expected behavior is always a plus.