Connect UDP sockets.

Allow Cobalt to connect UDP sockets. This saves kernel CPU time. In the download
benchmark page, this results in ~7% higher achieved bandwidth and ~5% less total
CPU usage.

net/socket/udp_socket_starboard.cc

@@ -162,7 +162,7 @@ int UDPSocketStarboard::GetLocalAddress(IPEndPoint* address) const {
 int UDPSocketStarboard::Read(IOBuffer* buf,
                              int buf_len,
                              CompletionOnceCallback callback) {
-  return RecvFrom(buf, buf_len, NULL, std::move(callback));
+  return RecvFrom(buf, buf_len, nullptr, std::move(callback));
 }
 
 int UDPSocketStarboard::RecvFrom(IOBuffer* buf,
@@ -271,17 +271,34 @@ int UDPSocketStarboard::InternalConnect(const IPEndPoint& address) {
   DCHECK(!remote_address_.get());
 
   int rv = 0;
-  // Cobalt does random bind despite bind_type_ because we do not connect
-  // UDP sockets but Chromium does. And if a socket does recvfrom() without
-  // any sendto() before, it needs to be bound to have a local port.
-  rv = RandomBind(address.GetFamily() == ADDRESS_FAMILY_IPV4 ?
-                      IPAddress::IPv4AllZeros() : IPAddress::IPv6AllZeros());
+  if (bind_type_ == DatagramSocket::RANDOM_BIND) {
+    // Construct IPAddress of appropriate size (IPv4 or IPv6) of 0s,
+    // representing INADDR_ANY or in6addr_any.
+    rv = RandomBind(address.GetFamily() == ADDRESS_FAMILY_IPV4
+                        ? IPAddress::IPv4AllZeros()
+                        : IPAddress::IPv6AllZeros());
+  }
 
   if (rv != OK)
     return rv;
 
+  SbSocketAddress storage;
+  if (!address.ToSbSocketAddress(&storage)) {
+    return ERR_ADDRESS_INVALID;
+  }
+
   remote_address_.reset(new IPEndPoint(address));
 
+  SbSocketError result = SbSocketConnect(socket_, &storage);
+  if (result != kSbSocketOk) {
+    return MapLastSocketError(socket_);
+  }
+
+  LOG(INFO) << __FUNCTION__
+            << " UDP CONNECT SUCCEEDED "
+               "================================================ "
+            << address;
+
   return OK;
 }
 
@@ -459,16 +476,16 @@ int UDPSocketStarboard::InternalRecvFrom(IOBuffer* buf,
                                          int buf_len,
                                          IPEndPoint* address) {
   SbSocketAddress sb_address;
-  int bytes_transferred =
-      SbSocketReceiveFrom(socket_, buf->data(), buf_len, &sb_address);
+  int bytes_transferred = SbSocketReceiveFrom(socket_, buf->data(), buf_len,
+                                              address ? &sb_address : nullptr);
   int result;
   if (bytes_transferred >= 0) {
     result = bytes_transferred;
     // Passing in NULL address is allowed. This is only to align with other
     // platform's implementation.
     if (address && !address->FromSbSocketAddress(&sb_address)) {
       result = ERR_ADDRESS_INVALID;
-    } else if (bytes_transferred == buf_len) {
+    } else if (bytes_transferred > buf_len) {
       result = ERR_MSG_TOO_BIG;
     }
   } else {
@@ -477,7 +494,8 @@ int UDPSocketStarboard::InternalRecvFrom(IOBuffer* buf,
 
   if (result != ERR_IO_PENDING) {
     IPEndPoint log_address;
-    if (result < 0 || !log_address.FromSbSocketAddress(&sb_address)) {
+    if (result < 0 || !address ||
+        !log_address.FromSbSocketAddress(&sb_address)) {
       LogRead(result, buf->data(), NULL);
     } else {
       LogRead(result, buf->data(), &log_address);