Add background color to gutter for breakpoints
Add background color to gutter for breakpoints

Add a background color to the linenumber gutter when setting a break-
point. This makes it easier to see at first glance for which line a
breakpoint was set.

Screenshots:
https://imgur.com/8Ev4eXV
https://imgur.com/H3ipmUt

Bug: chromium:1041830
Change-Id: I326a53b83b417ff928875da3cf3a0f4a00fdd027
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2194870
Commit-Queue: Wolfgang Beyer <573aa99bb19da47d816981118f95c945310dd3f4@chromium.org>
Reviewed-by: Mathias Bynens <17a2cbc4e33156874a9862b0f530521117e66a3d@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend