Update devtools:// security indicator and page info string

Change the page info string from "You're viewing a secure Google Chrome page"
to "You're viewing a developer tools page", since devtools pages are not necessarily
secure. Set the security indicator to display as neutral.

Screenshot: https://drive.google.com/file/d/1Q_BILWqvlUiCk3gIFYQCHhjZ2gAvhoau/view?usp=sharing

Bug: 980741
Change-Id: I57c3717ee628233a4a15d697815cdb7cf9455fa7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1709335
Commit-Queue: Livvie Lin <livvielin@chromium.org>
Reviewed-by: Emily Stark <estark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681967}
6 files changed