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/sync_buffer_unittest.cc b/modules/audio_coding/neteq/sync_buffer_unittest.cc
index f3f7895..ad04942 100644
--- a/modules/audio_coding/neteq/sync_buffer_unittest.cc
+++ b/modules/audio_coding/neteq/sync_buffer_unittest.cc
@@ -9,6 +9,7 @@
  */
 
 #include "modules/audio_coding/neteq/sync_buffer.h"
+#include "rtc_base/safe_conversions.h"
 
 #include "test/gtest.h"
 
@@ -57,7 +58,7 @@
   // Populate |new_data|.
   for (size_t channel = 0; channel < kChannels; ++channel) {
     for (size_t i = 0; i < kNewLen; ++i) {
-      new_data[channel][i] = i;
+      new_data[channel][i] = rtc::checked_cast<int16_t>(i);
     }
   }
   // Push back |new_data| into |sync_buffer|. This operation should pop out
@@ -97,7 +98,7 @@
   // Populate |new_data|.
   for (size_t channel = 0; channel < kChannels; ++channel) {
     for (size_t i = 0; i < kNewLen; ++i) {
-      new_data[channel][i] = 1000 + i;
+      new_data[channel][i] = rtc::checked_cast<int16_t>(1000 + i);
     }
   }
   sync_buffer.PushBack(new_data);
@@ -130,7 +131,7 @@
   // Populate |new_data|.
   for (size_t channel = 0; channel < kChannels; ++channel) {
     for (size_t i = 0; i < kNewLen; ++i) {
-      new_data[channel][i] = i;
+      new_data[channel][i] = rtc::checked_cast<int16_t>(i);
     }
   }
   // Push back |new_data| into |sync_buffer|. This operation should pop out