Removed the issue with the leading semicolon in the audio
processing module experiment description that was present
when AEC3 was not activated and when RefinedAdaptiveFilter
was activated.

BUG=webrtc:5778, webrtc:5777

Review URL: https://codereview.webrtc.org/1899123002

Cr-Commit-Position: refs/heads/master@{#12424}
diff --git a/webrtc/modules/audio_processing/echo_cancellation_impl.cc b/webrtc/modules/audio_processing/echo_cancellation_impl.cc
index c18ed94..5a7aef6 100644
--- a/webrtc/modules/audio_processing/echo_cancellation_impl.cc
+++ b/webrtc/modules/audio_processing/echo_cancellation_impl.cc
@@ -415,9 +415,9 @@
 
 std::string EchoCancellationImpl::GetExperimentsDescription() {
   rtc::CritScope cs(crit_capture_);
-  std::string description = (aec3_enabled_ ? "AEC3" : "");
+  std::string description = (aec3_enabled_ ? "AEC3;" : "");
   if (refined_adaptive_filter_enabled_) {
-    description += ";RefinedAdaptiveFilter";
+    description += "RefinedAdaptiveFilter;";
   }
   return description;
 }