Fixing warning C4267 on Win (more_configs).

This is a follow-up of https://webrtc-review.googlesource.com/c/src/+/12921.

Bug: chromium:759980
Change-Id: Ifd39adb6541c0c7e0337f587a8b34b84a07331ed
Reviewed-on: https://webrtc-review.googlesource.com/13122
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20341}
diff --git a/modules/audio_coding/neteq/expand_unittest.cc b/modules/audio_coding/neteq/expand_unittest.cc
index b52d626..aeaa07b 100644
--- a/modules/audio_coding/neteq/expand_unittest.cc
+++ b/modules/audio_coding/neteq/expand_unittest.cc
@@ -88,8 +88,8 @@
   void SetUp() override {
     // Fast-forward the input file until there is speech (about 1.1 second into
     // the file).
-    const size_t speech_start_samples =
-        static_cast<size_t>(test_sample_rate_hz_ * 1.1f);
+    const int speech_start_samples =
+        static_cast<int>(test_sample_rate_hz_ * 1.1f);
     ASSERT_TRUE(input_file_.Seek(speech_start_samples));
 
     // Pre-load the sync buffer with speech data.