Adding checks to guard against buffer overruns in QuotaFileIO::Write and base::FileUtilProxy::Write

base/file_util_proxy.cc

Index: base/file_util_proxy.cc
===================================================================
--- base/file_util_proxy.cc	(revision 96790)
+++ base/file_util_proxy.cc	(working copy)
@@ -866,6 +866,8 @@
     const char* buffer,
     int bytes_to_write,
     WriteCallback* callback) {
+  if (bytes_to_write <= 0)
+    return false;
   return Start(FROM_HERE, message_loop_proxy,
                new RelayWrite(file, offset, buffer, bytes_to_write, callback));
 }