Add an "append flag" to base::PlatformFile.

base/platform_file.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_PLATFORM_FILE_H_
 #define BASE_PLATFORM_FILE_H_
 
 #include "build/build_config.h"
 #if defined(OS_WIN)
 #include <windows.h>
 #endif
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/files/file_path.h"
 #include "base/time.h"
 
 namespace base {
 
 // PLATFORM_FILE_(OPEN|CREATE).* are mutually exclusive. You should specify

[jar (doing other things), 2013/06/04 23:31:50]

nit: you probably need an analogous comment about PLATFORM_FILE_WRITE and
PLATFORM_FILE_APPEND, along with your explanation.

 // exactly one of the five (possibly combining with other flags) when opening
 // or creating a file.
 enum PlatformFileFlags {
   PLATFORM_FILE_OPEN = 1 << 0,             // Opens a file, only if it exists.
   PLATFORM_FILE_CREATE = 1 << 1,           // Creates a new file, only if it
                                            // does not already exist.
   PLATFORM_FILE_OPEN_ALWAYS = 1 << 2,      // May create a new file.
   PLATFORM_FILE_CREATE_ALWAYS = 1 << 3,    // May overwrite an old file.
   PLATFORM_FILE_OPEN_TRUNCATED = 1 << 4,   // Opens a file and truncates it,
                                            // only if it exists.
   PLATFORM_FILE_READ = 1 << 5,
   PLATFORM_FILE_WRITE = 1 << 6,
   PLATFORM_FILE_EXCLUSIVE_READ = 1 << 7,   // EXCLUSIVE is opposite of Windows
                                            // SHARE
   PLATFORM_FILE_EXCLUSIVE_WRITE = 1 << 8,
   PLATFORM_FILE_ASYNC = 1 << 9,
   PLATFORM_FILE_TEMPORARY = 1 << 10,       // Used on Windows only
   PLATFORM_FILE_HIDDEN = 1 << 11,          // Used on Windows only
   PLATFORM_FILE_DELETE_ON_CLOSE = 1 << 12,
 
   PLATFORM_FILE_WRITE_ATTRIBUTES = 1 << 13,  // Used on Windows only
   PLATFORM_FILE_ENUMERATE = 1 << 14,         // May enumerate directory
 
   PLATFORM_FILE_SHARE_DELETE = 1 << 15,      // Used on Windows only
 
   PLATFORM_FILE_TERMINAL_DEVICE = 1 << 16,   // Serial port flags
   PLATFORM_FILE_BACKUP_SEMANTICS = 1 << 17,  // Used on Windows only
 
   PLATFORM_FILE_EXECUTE = 1 << 18,           // Used on Windows only
+
+  PLATFORM_FILE_APPEND = 1 << 19,

[jar (doing other things), 2013/06/04 23:31:50]

nit: You *might* want to re-order these, so that WRITE and APPEND are next to
each other, now that you've made them exclusive.

Do you think there is a bunch of other code that would break?  Are there other
consumers or exporters of these flags???

 };
 
 // PLATFORM_FILE_ERROR_ACCESS_DENIED is returned when a call fails because of
 // a filesystem restriction. PLATFORM_FILE_ERROR_SECURITY is returned when a
 // browser policy doesn't allow the operation to be executed.
 enum PlatformFileError {
   PLATFORM_FILE_OK = 0,
   PLATFORM_FILE_ERROR_FAILED = -1,
   PLATFORM_FILE_ERROR_IN_USE = -2,
   PLATFORM_FILE_ERROR_EXISTS = -3,
@@ skipping 178 matching lines @@
     return temp;
   }
 
  private:
   PlatformFile* value_;
 };
 
 }  // namespace base
 
 #endif  // BASE_PLATFORM_FILE_H_