Add SigslotTester0 for testing signals without argument.

BUG=

Review-Url: https://codereview.webrtc.org/2066443003
Cr-Original-Commit-Position: refs/heads/master@{#13141}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 4deba9adf141a4d08dae7ea1b5aa13dd8a22fbb0
2 files changed