Add a recipe to identify culprits for chromium compile failures.

scripts/slave/recipe_modules/chromium_tests/api.py

Index: scripts/slave/recipe_modules/chromium_tests/api.py
diff --git a/scripts/slave/recipe_modules/chromium_tests/api.py b/scripts/slave/recipe_modules/chromium_tests/api.py
index 7de07ebe0c8f2e99215ffb1678112a374609b2a0..88ab5e2e17064d62857992f7dee25db79d86b854 100644
--- a/scripts/slave/recipe_modules/chromium_tests/api.py
+++ b/scripts/slave/recipe_modules/chromium_tests/api.py
@@ -471,9 +471,15 @@ class ChromiumTestsApi(recipe_api.RecipeApi):
       # 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)