Make file system watcher compile on Mac OS 106, and add a runtime-call to test if the system suppor…

runtime/bin/file_system_watcher.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "bin/file_system_watcher.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 
 #include "include/dart_api.h"
 
 namespace dart {
 namespace bin {
 
 static const int kWatcherNativeField = 0;
 
 
 void SetWatcherIdNativeField(Dart_Handle watcher, intptr_t id) {
   ThrowIfError(Dart_SetNativeInstanceField(watcher, kWatcherNativeField, id));
 }
 
 
 void GetWatcherIdNativeField(Dart_Handle watcher, intptr_t* id) {
   ThrowIfError(Dart_GetNativeInstanceField(watcher, kWatcherNativeField, id));
 }
 
+void FUNCTION_NAME(FileSystemWatcher_IsSupported)(Dart_NativeArguments args) {
+  Dart_SetReturnValue(args, Dart_NewBoolean(FileSystemWatcher::IsSupported()));
+}
 
 void FUNCTION_NAME(FileSystemWatcher_WatchPath)(Dart_NativeArguments args) {
   Dart_Handle watcher = Dart_GetNativeArgument(args, 0);
   const char* path = DartUtils::GetStringValue(Dart_GetNativeArgument(args, 1));
   int events = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 2));
   bool recursive = DartUtils::GetBooleanValue(Dart_GetNativeArgument(args, 3));
   intptr_t id = FileSystemWatcher::WatchPath(path, events, recursive);
   if (id == -1) {
     Dart_PropagateError(DartUtils::NewDartOSError());
   } else {
@@ skipping 16 matching lines @@
   Dart_Handle watcher = Dart_GetNativeArgument(args, 0);
   intptr_t id;
   GetWatcherIdNativeField(watcher, &id);
   Dart_Handle handle = FileSystemWatcher::ReadEvents(id);
   ThrowIfError(handle);
   Dart_SetReturnValue(args, handle);
 }
 
 }  // namespace bin
 }  // namespace dart