Fix "value possibly truncated" warnings on MSVC, net/base edition.

net/base/network_change_notifier.cc

Index: net/base/network_change_notifier.cc
diff --git a/net/base/network_change_notifier.cc b/net/base/network_change_notifier.cc
index afd6b23d4fa2a0646ef30086ddfea1a86a0c5117..b952aa62e68a38541868b23996b281bcd0663bd4 100644
--- a/net/base/network_change_notifier.cc
+++ b/net/base/network_change_notifier.cc
@@ -305,7 +305,8 @@ class HistogramWatcher
     if (bytes_read > 10000 &&
         request_duration > base::TimeDelta::FromMilliseconds(1) &&
         request.creation_time() > last_connection_change_) {
-      int32 kbps = bytes_read * 8 / request_duration.InMilliseconds();
+      int32 kbps = static_cast<int32>(
+          bytes_read * 8 / request_duration.InMilliseconds());
       if (kbps > peak_kbps_since_last_connection_change_)
         peak_kbps_since_last_connection_change_ = kbps;
     }