Re-land socket refactor with fixes for Windows.

runtime/bin/file_system_watcher_linux.cc

Index: runtime/bin/file_system_watcher_linux.cc
diff --git a/runtime/bin/file_system_watcher_linux.cc b/runtime/bin/file_system_watcher_linux.cc
index e74c69fa062932e4a23c0c8429181efa3ed75a29..54f86cc8029ff43d1537b0758135cceed8772a09 100644
--- a/runtime/bin/file_system_watcher_linux.cc
+++ b/runtime/bin/file_system_watcher_linux.cc
@@ -110,7 +110,7 @@ Dart_Handle FileSystemWatcher::ReadEvents(intptr_t id, intptr_t path_id) {
   const intptr_t kEventSize = sizeof(struct inotify_event);
   const intptr_t kBufferSize = kEventSize + NAME_MAX + 1;
   uint8_t buffer[kBufferSize];
-  intptr_t bytes = Socket::Read(id, buffer, kBufferSize);
+  intptr_t bytes = SocketBase::Read(id, buffer, kBufferSize);
   if (bytes < 0) {
     return DartUtils::NewDartOSError();
   }