First step of porting VisitedLinkMaster to POSIX:

base/file_util.cc

Index: base/file_util.cc
diff --git a/base/file_util.cc b/base/file_util.cc
index 078e3afa2e5ac6c2271fb9436c18ec16d2e2db75..f21ff07a571f0a12708a1a0eb82ce60937a4e8be 100644
--- a/base/file_util.cc
+++ b/base/file_util.cc
@@ -276,6 +276,24 @@ bool CloseFile(FILE* file) {
   return fclose(file) == 0;
 }
 
+bool TruncateFile(FILE* file) {
+  if (file == NULL)
+    return false;
+  long current_offset = ftell(file);
+  if (current_offset == -1)
+    return false;
+#if defined(OS_WIN)
+  int fd = _fileno(file);
+  if (_chsize(fd, current_offset) != 0)
+    return false;
+#else
+  int fd = fileno(file);
+  if (ftruncate(fd, current_offset) != 0)
+    return false;
+#endif
+  return true;
+}
+
 bool ContainsPath(const FilePath &parent, const FilePath& child) {
   FilePath abs_parent = FilePath(parent);
   FilePath abs_child = FilePath(child);