DevTools: Label the more tabs button
DevTools: Label the more tabs button

When there are too many tabs to fit in the tab list, the button to see
more tabs was unlabeled.

Change-Id: Iadab77398a6bbf82d788d5a5e1cc0dc53ae1b589
Reviewed-on: https://chromium-review.googlesource.com/1188881
Reviewed-by: Andrey Lushnikov <73889f071ff743ad62763f13ff61c52ca3ee19d0@chromium.org>
Commit-Queue: Andrey Lushnikov <73889f071ff743ad62763f13ff61c52ca3ee19d0@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#586045}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 995c1fac672eae90b2630cde7c34297fed94b210
ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,dart-archive/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend