PCLF: Reserve vector before pushing.

Bug: None
Change-Id: I961f555085032330028b426e46a2c4ac576a2b03
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/260283
Commit-Queue: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36686}
diff --git a/api/test/peerconnection_quality_test_fixture.h b/api/test/peerconnection_quality_test_fixture.h
index 0e7d85a..4961fb5 100644
--- a/api/test/peerconnection_quality_test_fixture.h
+++ b/api/test/peerconnection_quality_test_fixture.h
@@ -422,6 +422,7 @@
     // subscribed to with specific resolution.
     std::vector<std::string> GetSubscribedPeers() const {
       std::vector<std::string> subscribed_streams;
+      subscribed_streams.reserve(peers_resolution_.size());
       for (const auto& entry : peers_resolution_) {
         subscribed_streams.push_back(entry.first);
       }