Google Chrome	69.0.3497.21 (Official Build) dev (64-bit)
Firmware Version	Google_Lulu.6301.136.57

This is a borderline bug/request. 

In Chrome://bookmarks, you can use arrow keys to move up and down the bookmarks list. However, it's limited in what you can see, for example, the left side of the bookmark with the relevant text are off the magnifier screen. With a mouse, you could move the focus over to the left. However, there is no way to do this with keyboard only. 

This is similar but different to this feature request to adjust docked magnifier zoom levels via keyboard only. 
https://bugs.chromium.org/p/chromium/issues/detail?id=865255