Modified PressEnterToContinue() to actualy check if Enter is pressed

Modified PressEnterToContinue() to run the Windows message loop in the
context of the SingleThreadedTaskQueueForTesting thread. The previous
PressEnterToContinue() was running the message loop in the context of
the main thread, but the "Local Preview" and "Loopback Video #0" are
created in the context of the SingleThreadedTaskQueueForTesting thread
and the message loop must be executed in the context of the thread that
created these windows in order for these windows to respond to any
event.

BUG=webrtc:9123

Change-Id: I2ec19f2569a940a510d3b2bd3881a89032d70332
Reviewed-on: https://webrtc-review.googlesource.com/c/67520
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25408}
diff --git a/AUTHORS b/AUTHORS
index e24dd51..c85a4e8 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -16,6 +16,7 @@
 Colin Plumb
 David Porter <david@porter.me>
 Dax Booysen <dax@younow.com>
+Danail Kirov <dkirovbroadsoft@gmail.com>
 Dmitry Lizin <sdkdimon@gmail.com>
 Eric Rescorla, RTFM Inc. <ekr@rtfm.com>
 Frederik Riedel, Frogg GmbH <frederik.riedel@frogg.io>