Support length operation without opening 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 44 matching lines @@
     kCreateRequest = 1,
     kDeleteRequest = 2,
     kOpenRequest = 3,
     kFullPathRequest = 4,
     kDirectoryRequest = 5,
     kCloseRequest = 6,
     kPositionRequest = 7,
     kSetPositionRequest = 8,
     kTruncateRequest = 9,
     kLengthRequest = 10,
-    kFlushRequest = 11,
-    kReadByteRequest = 12,
-    kWriteByteRequest = 13,
-    kReadListRequest = 14,
-    kWriteListRequest = 15,
-    kWriteStringRequest = 16
+    kLengthFromNameRequest = 11,
+    kFlushRequest = 12,
+    kReadByteRequest = 13,
+    kWriteByteRequest = 14,
+    kReadListRequest = 15,
+    kWriteListRequest = 16,
+    kWriteStringRequest = 17
   };
 
   ~File();
 
   // Read/Write attempt to transfer num_bytes to/from buffer. It returns
   // the number of bytes read/written.
   int64_t Read(void* buffer, int64_t num_bytes);
   int64_t Write(const void* buffer, int64_t num_bytes);
 
   // ReadFully and WriteFully do attempt to transfer num_bytes to/from
@@ skipping 35 matching lines @@
   // mode contains kTruncate.
   static File* Open(const char* name, FileOpenMode mode);
 
   // Create a file object for the specified stdio file descriptor
   // (stdin, stout or stderr).
   static File* OpenStdio(int fd);
 
   static bool Exists(const char* name);
   static bool Create(const char* name);
   static bool Delete(const char* name);
+  static off_t LengthFromName(const char* name);
   static bool IsAbsolutePath(const char* pathname);
   static char* GetCanonicalPath(const char* name);
   static char* GetContainingDirectory(char* name);
   static const char* PathSeparator();
   static const char* StringEscapedPathSeparator();
   static StdioHandleType GetStdioHandleType(int fd);
 
   static FileOpenMode DartModeToFileMode(DartFileOpenMode mode);
 
   static Dart_Port GetServicePort();
@@ skipping 12 matching lines @@
   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_