Run auto-spell-checker (codespell) on files in depot_tools.

This should only change spelling in:
 - messages that are printed
 - comments
 - docstrings

Review-Url: https://codereview.chromium.org/2277513002
diff --git a/git_common.py b/git_common.py
index 0fd1e7f..162cc85 100644
--- a/git_common.py
+++ b/git_common.py
@@ -900,7 +900,7 @@
 
   Args:
     treeref (str) - a git ref which resolves to a tree (commits count as trees).
-    recurse (bool) - include all of the tree's decendants too. File names will
+    recurse (bool) - include all of the tree's descendants too. File names will
       take the form of 'some/path/to/file'.
 
   Return format: