How can I prevent shift selection from expanding?

On Yosemite in current Chrome (and random other places, but let's try to just solve it in Chrome), if i selection some text (say the "sk differ" in "ask different"), then hold shift and press right arrow, it will expand the selection to include the next character to the right (selection becomes "sk differe"). If i then press left arrow, i'd like the selection to (again) become "sk differ". Instead, in some apps (at least Chrome), it becomes "ask differe". So it seems that it will only expand the selection, so pressing either arrow key only grows the corresponding end of the selection.

How can i make it so that it selects from a caret position that is at either end of the selection (NOT both)?