Misc truncation fixes for gn builds with VS 2015

content/browser/renderer_host/p2p/socket_host_test_utils.cc

Index: content/browser/renderer_host/p2p/socket_host_test_utils.cc
diff --git a/content/browser/renderer_host/p2p/socket_host_test_utils.cc b/content/browser/renderer_host/p2p/socket_host_test_utils.cc
index 1f56903c558dfb202f921a0a9b173b6827be83f2..36dc2eec9974547b3fddc314bda496b7c131df7d 100644
--- a/content/browser/renderer_host/p2p/socket_host_test_utils.cc
+++ b/content/browser/renderer_host/p2p/socket_host_test_utils.cc
@@ -196,8 +196,8 @@ void CreateRandomPacket(std::vector<char>* packet) {
 static void CreateStunPacket(std::vector<char>* packet, uint16 type) {
   CreateRandomPacket(packet);
   *reinterpret_cast<uint16*>(&*packet->begin()) = base::HostToNet16(type);
-  *reinterpret_cast<uint16*>(&*packet->begin() + 2) =
-      base::HostToNet16(packet->size() - kStunHeaderSize);
+  *reinterpret_cast<uint16*>(&*packet->begin() + 2) = base::HostToNet16(
+      base::checked_cast<uint16>(packet->size() - kStunHeaderSize));
   *reinterpret_cast<uint32*>(&*packet->begin() + 4) =
       base::HostToNet32(kStunMagicCookie);
 }