[builders.py] Add comment to _deps_builders about duplicated mappings

Mac10.6 (deps) is used for all mac ports.

R=dpranke
BUG=none

Review URL: https://codereview.chromium.org/690943002

git-svn-id: svn://svn.chromium.org/blink/trunk@184897 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/builders.py

@@ -65,6 +65,8 @@ _deps_builders = {
     "win-xp": "WebKit XP (deps)",
     "win-win7": "WebKit XP (deps)",
     "mac-snowleopard": "WebKit Mac10.6 (deps)",
+    # The following port names are mapped to 10.6 bot since we don't have bots
+    # for these ports.
     "mac-lion": "WebKit Mac10.6 (deps)",
     "mac-mountainlion": "WebKit Mac10.6 (deps)",
     "mac-mavericks": "WebKit Mac10.6 (deps)",