Add more builders to blacklist to //testing/buildbot/manage.py.

This is to help the automation of converting tests to be isolated and run on
Swarming instead of locally.

R=jam@chromium.org
BUG=98637

Review URL: https://codereview.chromium.org/1166993003

Cr-Commit-Position: refs/heads/master@{#333106}

testing/buildbot/manage.py

@@ -36,6 +36,14 @@ SKIP = {
   # http://crbug.com/441429
   'Linux Trusty (32)', 'Linux Trusty (dbg)(32)',
 
+  # http://crbug.com/480053
+  'Linux GN',
+  'linux_chromium_gn_rel',
+
+  # Unmaintained builders on chromium.fyi
+  'ClangToTMac',
+  'ClangToTMacASan',
+
   # One off builders. Note that Swarming does support ARM.
   'Linux ARM Cross-Compile',
   'Site Isolation Linux',