Fix incorrect variable shadowing
Fix incorrect variable shadowing

The underscore migration of Ruler in https://crrev.com/c/3085187
resulted in a bug, where the Ruler's contentElement was
incorrectly shadowing the parent's contentElement instead of referring
to its own member variable.

Bug: chromium:1207342
Change-Id: I5bffffa758c3f35873647b238db5d2668ca2965b
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/3103228
Commit-Queue: Jan Scheffler <8abd9e3d93041d096604cb2a1b3070dd7075ba7b@chromium.org>
Commit-Queue: Simon Zünd <38944668e9e2ca98ccd0275b53370f90fa55c113@chromium.org>
Auto-Submit: Jan Scheffler <8abd9e3d93041d096604cb2a1b3070dd7075ba7b@chromium.org>
Reviewed-by: Simon Zünd <38944668e9e2ca98ccd0275b53370f90fa55c113@chromium.org>
Reviewed-by: Tim van der Lippe <dba8716ee7f8d16236046f74d2167cb94410f6ed@chromium.org>

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