Make MessageQueue processing an optional feature of FakeClock

This is used to avoid thread processing in simulated time
controller. This saves up to 30% execution time in debug builds.

Bug: webrtc:10365
Change-Id: Ie83dfb2468d371e4687d28c776acf7e23eb411d1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/133173
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27666}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 59eca29..e7ad807 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -1084,6 +1084,7 @@
     ":checks",
     ":rtc_base",
     "../api/units:time_delta",
+    "../api/units:timestamp",
     "memory:fifo_buffer",
     "third_party/sigslot",
     "//third_party/abseil-cpp/absl/algorithm:container",