Separate lines added via post upload from original description

BUG=skia:6598
NOTRY=true

Change-Id: I23fa415788e91da01d33ab3ab912aa420636574c
Reviewed-on: https://skia-review.googlesource.com/15869
Commit-Queue: Ravi Mistry <rmistry@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 0baf69c..768892a 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -539,6 +539,8 @@
 
     # If the description has changed update it.
     if new_description_lines != original_description_lines:
+      # Add a new line separating the new contents from the old contents.
+      new_description_lines.insert(len(original_description_lines), '')
       cl.UpdateDescriptionFooters(new_description_lines, footers)
 
     return results