[Underscore Migration] Migrate core/workspace_diff
[Underscore Migration] Migrate core/workspace_diff

This patch is part of the underscore migration that adds the private
keyword to all properties that start with an underscore and removes the
underscore.

Bug:chromium:1207342
Change-Id: I178157fd5f54c1aa7a8d4bee6fe2fbc6ae972b5c
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/3078242
Auto-Submit: Jan Scheffler <8abd9e3d93041d096604cb2a1b3070dd7075ba7b@chromium.org>
Reviewed-by: Tim van der Lippe <dba8716ee7f8d16236046f74d2167cb94410f6ed@chromium.org>
Commit-Queue: Jan Scheffler <8abd9e3d93041d096604cb2a1b3070dd7075ba7b@chromium.org>

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