WebRTC-DeprecateGlobalFieldTrialString/Enabled/ - part 4/inf

convert almost all of video/ (and the collateral)

Bug: webrtc:10335
Change-Id: Ic94e05937f54d11ee8a635b6b66fd146962d9f11
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/254601
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36192}
diff --git a/test/scoped_key_value_config.cc b/test/scoped_key_value_config.cc
index fe3f426..723be22 100644
--- a/test/scoped_key_value_config.cc
+++ b/test/scoped_key_value_config.cc
@@ -66,8 +66,11 @@
                                            const std::string& s)
     : parent_(parent), leaf_(nullptr) {
   InsertIntoMap(key_value_map_, s);
-  // Also store field trials in global string (until we get rid of it).
-  scoped_field_trials_ = std::make_unique<ScopedFieldTrials>(s);
+
+  if (!s.empty()) {
+    // Also store field trials in global string (until we get rid of it).
+    scoped_field_trials_ = std::make_unique<ScopedFieldTrials>(s);
+  }
 
   if (parent == nullptr) {
     // We are root, set leaf_.