Fix windows build

runtime/bin/dartutils.cc

Index: runtime/bin/dartutils.cc
diff --git a/runtime/bin/dartutils.cc b/runtime/bin/dartutils.cc
index 673e607393a9c3d47c0c0bf1359a3dcaf9b09d2b..9e263051f57bf8a9a48ac5da8d328f3cc120d94a 100644
--- a/runtime/bin/dartutils.cc
+++ b/runtime/bin/dartutils.cc
@@ -269,7 +269,7 @@ static uint8_t* SocketReadUntilEOF(intptr_t socket, intptr_t* response_len) {
   ASSERT(buffer != NULL);
   intptr_t buffer_cursor = 0;
   do {
-    ssize_t bytes_read = Socket::Read(socket, &buffer[buffer_cursor],
+    int bytes_read = Socket::Read(socket, &buffer[buffer_cursor],
                                       buffer_size - buffer_cursor - 1);
     if (bytes_read < 0) {
       free(buffer);