Move safe_conversions.h to webrtc namespace

Bug: webrtc:42232595
Change-Id: I4145233e74fc684539d493423cafe142159fe8ff
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/378720
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Evan Shrubsole <eshr@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43973}
diff --git a/modules/audio_coding/neteq/audio_multi_vector_unittest.cc b/modules/audio_coding/neteq/audio_multi_vector_unittest.cc
index 386c3d4..eaf3147 100644
--- a/modules/audio_coding/neteq/audio_multi_vector_unittest.cc
+++ b/modules/audio_coding/neteq/audio_multi_vector_unittest.cc
@@ -47,7 +47,7 @@
     // And so on.
     for (size_t i = 0; i < array_length(); ++i) {
       for (size_t j = 1; j <= num_channels_; ++j) {
-        *ptr = rtc::checked_cast<int16_t>(j * 100 + i);
+        *ptr = checked_cast<int16_t>(j * 100 + i);
         ++ptr;
       }
     }