Added linux_gpu to the default set of try servers.

This configuration is already experimentally receiving 100% of the
Chromium and Blink CQs' load. Expand its testing to cover manually
submitted try jobs as well.

As a side-effect, added multi-master support to GetDefaultTryConfigs.
Tested manually.

BUG=327170

Review URL: https://codereview.chromium.org/242963003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@265455 0039d316-1c4b-4281-b951-d872f2087c98

PRESUBMIT.py

@@ -1261,6 +1261,16 @@ def CheckChangeOnUpload(input_api, output_api):
   return results
 
 
+def GetTryServerMasterForBot(bot):
+  """Returns the Try Server master for the given bot.
+
+  Assumes that most Try Servers are on the tryserver.chromium master."""
+  non_default_master_map = {
+      'linux_gpu': 'tryserver.chromium.gpu',
+  }
+  return non_default_master_map.get(bot, 'tryserver.chromium')
+
+
 def GetDefaultTryConfigs(bots=None):
   """Returns a list of ('bot', set(['tests']), optionally filtered by [bots].
 
@@ -1329,6 +1339,7 @@ def GetDefaultTryConfigs(bots=None):
       'linux_chromium_compile_dbg': ['defaulttests'],
       'linux_chromium_rel': ['defaulttests'],
       'linux_chromium_clang_dbg': ['defaulttests'],
+      'linux_gpu': ['defaulttests'],
       'linux_nacl_sdk_build': ['compile'],
       'linux_rel': [
           'telemetry_perf_unittests',
@@ -1394,16 +1405,18 @@ def GetDefaultTryConfigs(bots=None):
                                  for x in builders_and_tests[bot]]
 
   if bots:
-    return {
-        'tryserver.chromium': dict((bot, set(builders_and_tests[bot]))
-                                   for bot in bots)
-    }
+    filtered_builders_and_tests = dict((bot, set(builders_and_tests[bot]))
+                                       for bot in bots)
   else:
-    return {
-        'tryserver.chromium': dict(
-            (bot, set(tests))
-            for bot, tests in builders_and_tests.iteritems())
-    }
+    filtered_builders_and_tests = dict(
+        (bot, set(tests))
+        for bot, tests in builders_and_tests.iteritems())
+
+  # Build up the mapping from tryserver master to bot/test.
+  out = dict()
+  for bot, tests in filtered_builders_and_tests.iteritems():
+    out.setdefault(GetTryServerMasterForBot(bot), {})[bot] = tests
+  return out
 
 
 def CheckChangeOnCommit(input_api, output_api):
@@ -1456,6 +1469,7 @@ def GetPreferredTryMasters(project, change):
       'linux_chromium_chromeos_rel',
       'linux_chromium_clang_dbg',
       'linux_chromium_rel',
+      'linux_gpu',
       'mac_chromium_compile_dbg',
       'mac_chromium_rel',
       'win_chromium_compile_dbg',