Add AFDO to nightly builds.

This adds an option, '--use_afdo' to build_chromeos.py, along with
a list of boards for which it is valid. The flag will cause
build_chromeos.py to add 'USE=afdo_use' to calls to build_packages,
if the board is appropriate. This CL also updates test_toolchains.py
to pass --use_afdo to build_chromeos, if appropriate.

BUG=None
TEST=Tried it in my own directory and it worked.

Change-Id: I0a2056f86783dbd30a2fd650729c888fd1df1f67
Reviewed-on: https://chrome-internal-review.googlesource.com/169174
Reviewed-by: Luis Lozano <llozano@chromium.org>
Commit-Queue: Caroline Tice <cmtice@google.com>
Tested-by: Caroline Tice <cmtice@google.com>
diff --git a/test_toolchains.py b/test_toolchains.py
index aae035a..578312e 100644
--- a/test_toolchains.py
+++ b/test_toolchains.py
@@ -13,6 +13,7 @@
 
 
 WEEKLY_REPORTS_ROOT="/usr/local/google/crostc/weekly_test_data"
+AFDO_BOARDS = ["butterfly", "lumpy", "stumpy", "stout", "parrot", "parrot_ivb"]
 
 class GCCConfig(object):
   def __init__(self, githash):
@@ -76,6 +77,9 @@
       if self._public:
         build_chromeos_args.append("--env=USE=-chrome_internal")
 
+      if self._board in AFDO_BOARDS:
+        build_chromeos_args.append("--env=USE=afdo_use")
+
       ret = build_chromeos.Main(build_chromeos_args)
       if ret:
         raise Exception("Couldn't build ChromeOS!")