Add a recipe to identify culprits for chromium compile failures.

scripts/slave/recipe_modules/chromium_tests/api.py

 # Copyright 2014 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.
 
 import ast
 import contextlib
 import copy
 import itertools
 import json
 
@@ skipping 453 matching lines @@
           mode='dev'
       )
 
   def run_mb_and_compile(self, compile_targets, isolated_targets, name_suffix):
     if self.m.chromium.c.project_generator.tool == 'mb':
       # We don't use the mastername and buildername passed in, because
       # those may be the values of the continuous builder the trybot may
       # be configured to match; we need to use the actual mastername
       # and buildername we're running on, because it may be configured
       # with different MB settings.
-      real_mastername = self.m.properties['mastername']
-      real_buildername = self.m.properties['buildername']
-      self.m.chromium.run_mb(real_mastername, real_buildername,
+      # However, use target_mastername and target_buildername instead if they
+      # are available in the build properties. This gives a recipe running on a
+      # trybot the flexibility to run MB in exactly the same configuration as
+      # the continuous builder it tries to match.
+      target_mastername = self.m.properties.get('target_mastername') or \
+          self.m.properties['mastername']
+      target_buildername = self.m.properties.get('target_buildername') or \
+          self.m.properties['buildername']

[Dirk Pranke, 2015/11/17 22:38:51]

nit: wrap the expression in parentheses instead of using line continuations,
e.g.:

target_mastername = (self.m... or
                     self.m...)

[stgao, 2015/11/19 22:06:33]

Done.

+      self.m.chromium.run_mb(target_mastername, target_buildername,
                              isolated_targets=isolated_targets,
                              name='generate_build_files%s' % name_suffix)
 
     self.m.chromium.compile(compile_targets, name='compile%s' % name_suffix)
 
   def tests_for_builder(self, mastername, buildername, update_step, master_dict,
                         override_bot_type=None):
     got_revision = update_step.presentation.properties['got_revision']
 
     bot_config = master_dict.get('builders', {}).get(buildername)
@@ skipping 340 matching lines @@
       result_text = 'MB is enabled for this builder at this revision.'
       log_name = 'Builder MB-ready'
       self.m.step.active_result.presentation.logs[log_name] = [result_text]
       return False
     except (self.m.step.StepFailure, KeyError):
       result_text = 'MB is not enabled for this builder at this revision.'
       log_name = 'Builder NOT MB-ready'
       self.m.step.active_result.presentation.logs[log_name] = [result_text]
       self.m.step.active_result.presentation.status = self.m.step.WARNING
       return True