[fuchsia] Fix build. Build packages/ output. Add Directory::Exists().

runtime/vm/os_fuchsia.cc

 // Copyright (c) 2016, 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 "vm/globals.h"
 #if defined(TARGET_OS_FUCHSIA)
 
 #include "vm/os.h"
 
 #include <errno.h>
@@ skipping 137 matching lines @@
   UNIMPLEMENTED();
   return false;
 }
 
 
 int OS::NumberOfAvailableProcessors() {
   return sysconf(_SC_NPROCESSORS_CONF);
 }
 
 
+uintptr_t OS::MaxRSS() {
+  UNIMPLEMENTED();
+  return 0;
+}
+
+
 void OS::Sleep(int64_t millis) {
   mx_nanosleep(
       millis * kMicrosecondsPerMillisecond * kNanosecondsPerMicrosecond);
 }
 
 
 void OS::SleepMicros(int64_t micros) {
   mx_nanosleep(
       micros * kNanosecondsPerMicrosecond);
 }
@@ skipping 134 matching lines @@
 }
 
 
 void OS::Exit(int code) {
   UNIMPLEMENTED();
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_FUCHSIA)