Let GetPreferredTryMasters read from CQ config.

PRESUBMIT.py

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Top-level presubmit script for Blink.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
@@ skipping 326 matching lines @@
     results.extend(input_api.canned_checks.CheckTreeIsOpen(
         input_api, output_api,
         json_url='http://blink-status.appspot.com/current?format=json'))
     results.extend(input_api.canned_checks.CheckChangeHasDescription(
         input_api, output_api))
     results.extend(_CheckSubversionConfig(input_api, output_api))
     return results
 
 
 def GetPreferredTryMasters(project, change):
-    return {
-        'tryserver.blink': {
-            'android_blink_compile_dbg': set(['defaulttests']),
-            'android_blink_compile_rel': set(['defaulttests']),
-            'android_chromium_gn_compile_rel': set(['defaulttests']),
-            'linux_blink_compile_dbg': set(['defaulttests']),
-            'linux_blink_rel': set(['defaulttests']),
-            'linux_chromium_gn_rel': set(['defaulttests']),
-            'mac_blink_compile_dbg': set(['defaulttests']),
-            'mac_blink_rel': set(['defaulttests']),
-            'win_blink_compile_dbg': set(['defaulttests']),
-            'win_blink_rel': set(['defaulttests']),
-        },
-    }
+    import json
+    import os.path
+    import platform
+    import subprocess
+
+    cq_config_path = os.path.join(
+        change.RepositoryRoot(), 'infra', 'config', 'cq.cfg')
+    # commit_queue.py below is a script in depot_tools directory, which has a
+    # 'builders' command to retrieve a list of CQ builders from the CQ config.
+    is_win = platform.system() == 'Windows'
+    masters = json.loads(subprocess.check_output(
+        ['commit_queue', 'builders', cq_config_path], shell=is_win))
+
+    try_config = {}
+    for master in masters:
+        try_config.setdefault(master, {})
+        for builder in masters[master]:
+            # Do not trigger presubmit builders, since they're likely to fail
+            # (e.g. OWNERS checks before finished code review), and we're
+            # running local presubmit anyway.
+            if 'presubmit' not in builder:
+                try_config[master][builder] = ['defaulttests']
+
+    return try_config