[clang-tidy] Apply performance-for-range-copy fixes.

This CL applies clang-tidy's performance-for-range-copy [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-for-range-copy.html

Bug: webrtc:10215
Change-Id: I7c83290b8866d76129bbec4e24e6701f5014102e
Reviewed-on: https://webrtc-review.googlesource.com/c/120043
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26420}

pc/peer_connection_interface_unittest.cc

@@ -2664,7 +2664,7 @@ TEST_P(PeerConnectionInterfaceTest, CloseAndTestStreamsAndStates) {
   } else {
     // Verify that the RtpTransceivers are still present but all stopped.
     EXPECT_EQ(2u, pc_->GetTransceivers().size());
-    for (auto transceiver : pc_->GetTransceivers()) {
+    for (const auto& transceiver : pc_->GetTransceivers()) {
       EXPECT_TRUE(transceiver->stopped());
     }
   }