Truncate the download file name if it exceeds the filesystem limit.

base/sys_info.h

Index: base/sys_info.h
diff --git a/base/sys_info.h b/base/sys_info.h
index 97b17c4a0afd6db7ca1fbaab638faeb3615dbbd7..21514e20c0e57ac4d9cd69e57398e78d44c8ad4b 100644
--- a/base/sys_info.h
+++ b/base/sys_info.h
@@ -35,6 +35,10 @@ class BASE_EXPORT SysInfo {
   // or -1 on failure.
   static int64 AmountOfFreeDiskSpace(const FilePath& path);
 
+  // Return the maximum length of path component on the volume containing
+  // |path| in the number of FilePath::CharType, or -1 on failure.
+  static int GetMaximumPathComponentLength(const FilePath& path);
+
   // Returns system uptime in milliseconds.
   static int64 Uptime();