(zoom in to fit more text)
Chrome calls it zooming in. As does pretty much any program that fiddles with pictures.
Zoom is when something far away is made to look closer. I suppose the term has also been adopted for webpages and other documents, but the main idea is still that the item is not actually changing size, it's just your view of it that is changing. Image viewing programs could also let you zoom in on a picture, making it appear larger, but the image itself still has the same dimensions.
To fit more readable text on an image, you actually need to increase the pixel size of the image. When you do this, it is scaling, not zooming. So for example, in Photoshop, I can open a 300x300 image. I could then zoom in and the image will take up twice as much space on my screen, but it is still 300x300. But I could then go and change the image size to 600x600, which would be called scaling the image.