Interestingly enough, prior to Indian Summer I had no scroll arrows in Chromium but arrows in Iceweasel. I just thought it was a Chromium or QT/GTK thing. I generally use the touchpad or mouse wheel anyway, so it is no real issue.
Since I have done the clean install of Indian Summer and Plasma 5, I have the opposite situation. I have arrows in Chromium, but none in Iceweasel. If I grab the bar with the mouse the bar changes to a blue color and I can drag it up and down. If I open a KDE app (Kate and Gwenview specifically) I see the same bar but also arrows shaped like the theme caret style ( ^ ). In Chrome I see a full triangle.
I use apt-upgrade (seldom) more often a dist-upgrade and never an upgrade. KDE-Standard was installed.