Rename method to IsEmpty for Worklist. IsGlobalEmpty is easy to
confuse with IsGlobalPoolEmpty.

Change-Id: Id9744cef2630f7c0642ec37ef9a18296acee87e3
Reviewed-on: https://chromium-review.googlesource.com/1115222
Commit-Queue: Dominik Inführ <dinfuehr@google.com>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54153}