Adding guards against heap overflow in PPB_FileIO::Read

base/file_util_proxy.cc

Index: base/file_util_proxy.cc
===================================================================
--- base/file_util_proxy.cc	(revision 97034)
+++ base/file_util_proxy.cc	(working copy)
@@ -854,6 +854,8 @@
     int64 offset,
     int bytes_to_read,
     ReadCallback* callback) {
+  if (bytes_to_read < 0)
+    return false;
   return Start(FROM_HERE, message_loop_proxy,
                new RelayRead(file, offset, bytes_to_read, callback));
 }