Add error handling to random access file

runtime/bin/file.h

 // Copyright (c) 2012, 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.
 
 #ifndef BIN_FILE_H_
 #define BIN_FILE_H_
 
 #if defined(_WIN32)
 typedef signed __int64 int64_t;
 typedef unsigned __int8 uint8_t;
@@ skipping 84 matching lines @@
   // Returns a negative value if position cannot be determined.
   off_t Position();
 
   // Set the byte position in the file.
   bool SetPosition(int64_t position);
 
   // Truncate (or extend) the file to the given length in bytes.
   bool Truncate(int64_t length);
 
   // Flush contents of file.
-  void Flush();
+  bool Flush();
+
+  // Returns whether the file has been closed.
+  bool IsClosed();
 
   const char* name() const { return name_; }
 
   // Open the file with the given name. The file is always opened for
   // reading. If mode contains kWrite the file is opened for both
   // reading and writing. If mode contains kWrite and the file does
   // not exist the file is created. The file is truncated to length 0 if
   // mode contains kTruncate.
   static File* Open(const char* name, FileOpenMode mode);
 
@@ skipping 11 matching lines @@
   static const char* StringEscapedPathSeparator();
   static StdioHandleType GetStdioHandleType(int fd);
 
   static FileOpenMode DartModeToFileMode(DartFileOpenMode mode);
 
   static Dart_Port GetServicePort();
 
  private:
   File(const char* name, FileHandle* handle) : name_(name), handle_(handle) { }
   void Close();
-  bool IsClosed();
 
   static const int kClosedFd = -1;
 
   const char* name_;
   // FileHandle is an OS specific class which stores data about the file.
   FileHandle* handle_;  // OS specific handle for the file.
 
   // DISALLOW_COPY_AND_ASSIGN(File).
   File(const File&);
   void operator=(const File&);
 
   static dart::Mutex mutex_;
   static int service_ports_size_;
   static Dart_Port* service_ports_;
   static int service_ports_index_;
 };
 
 #endif  // BIN_FILE_H_