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

base/sys_info_posix.cc

Index: base/sys_info_posix.cc
diff --git a/base/sys_info_posix.cc b/base/sys_info_posix.cc
index f2119cd7fdb538ebc34699088387aa2381e8cc4e..e7664caa356069ace4a18aa50bf6c534c408b943 100644
--- a/base/sys_info_posix.cc
+++ b/base/sys_info_posix.cc
@@ -50,6 +50,12 @@ int64 SysInfo::AmountOfFreeDiskSpace(const FilePath& path) {
   return static_cast<int64>(stats.f_bavail) * stats.f_frsize;
 }
 
+// static
+int SysInfo::GetMaximumPathComponentLength(const FilePath& path) {
+  base::ThreadRestrictions::AssertIOAllowed();
+  return pathconf(path.value().c_str(), _PC_NAME_MAX);
+}
+
 #if !defined(OS_MACOSX) && !defined(OS_ANDROID)
 // static
 std::string SysInfo::OperatingSystemName() {