[clang-tidy] Apply performance-inefficient-vector-operation fixes.

This CL applies clang-tidy's performance-inefficient-vector-operation
[1] on the WebRTC codebase.

All changes in this CL are automatically generated by both clang-tidy
and 'git cl format'.

[1] - https://clang.llvm.org/extra/clang-tidy/checks/performance-inefficient-vector-operation.html

Bug: webrtc:10252
Change-Id: I824caab2a5746036852e00d714b89aa5ec030ee3
Reviewed-on: https://webrtc-review.googlesource.com/c/120052
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26442}
diff --git a/rtc_base/fake_ssl_identity.cc b/rtc_base/fake_ssl_identity.cc
index 8607e0a..480922c 100644
--- a/rtc_base/fake_ssl_identity.cc
+++ b/rtc_base/fake_ssl_identity.cc
@@ -75,6 +75,7 @@
 
 FakeSSLIdentity::FakeSSLIdentity(const std::vector<std::string>& pem_strings) {
   std::vector<std::unique_ptr<SSLCertificate>> certs;
+  certs.reserve(pem_strings.size());
   for (const std::string& pem_string : pem_strings) {
     certs.push_back(absl::make_unique<FakeSSLCertificate>(pem_string));
   }