Don't set fastbuild=1 for Mac ASan trybots.

scripts/slave/recipe_modules/chromium/config.py

Index: scripts/slave/recipe_modules/chromium/config.py
diff --git a/scripts/slave/recipe_modules/chromium/config.py b/scripts/slave/recipe_modules/chromium/config.py
index c34750a5fe82b2868dcd7feb3904bfb6caaa9969..1a1fcb5f3733fb94a605792dc15d1d74f924158a 100644
--- a/scripts/slave/recipe_modules/chromium/config.py
+++ b/scripts/slave/recipe_modules/chromium/config.py
@@ -453,7 +453,9 @@ def _memory_tool(c, tool):
 
 @config_ctx()
 def trybot_flavor(c):
-  fastbuild(c, optional=True)
+  if not (c.TARGET_PLATFORM == 'mac' and
+          c.gyp_env.GYP_DEFINES.get('asan', 0)):

[Paweł Hajdan Jr., 2015/01/27 13:57:19]

This is potentially fragile. Expectations show us that it seems to behave
correctly for now, but AFAICT nothing prevents people from e.g. accidentally
calling fastbuild after this, or adding asan config after trybot_flavor.

In other words, this depends on order of applying configs, which I'd prefer to
avoid. This seems to be the only place where we call GYP_DEFINES.get in a
config.py file, and I'd like to avoid introducing the first case.

Robbie, Aaron: what would be your recommendations? I'm quite concerned the
recipe configs in their current shape may make maintainability harder.

[iannucci, 2015/01/30 01:21:00]

Configs are definitely allowed to introspect themselves, the .get is fine.

The config (that is: `c`) actually stores a list of config functions which have
already been applied, and prevents you from applying the same config function
from being applied twice. The 'optional=True' here is actually specifying that
'fastbuild' NOT be added to this internal list.

What's the intended behavior here? IIUC you want to conditionally apply it, and
then ban it from ever being applied to this config. You could do this by
removing the optional=True, and then making an else case which adds it to the
banlist (don't remember how this is done off the top of my head, it may be an
internal api that we have to make public).

[Alexander Potapenko, 2015/01/30 10:29:00]

That's nice to know, thank you.
Well, my intention was to at least remove fastbuild=1 from the ASan Mac trybot
configs.
This CL solves that particular task, but I agree that other configs may still
change the fastbuild setting.
What if I just add fastbuild=0 in the else case? That'll be the same "fastbuild"
config, so nobody'll change the fastbuild setting on top of that.

+    fastbuild(c, optional=True)
   dcheck(c, optional=True)
 
 @config_ctx()