Turn on --fast on official builds.

parallel_emerge

Index: parallel_emerge
diff --git a/parallel_emerge b/parallel_emerge
index c912a115ac000207582caa693c4997e429764990..ce40be4b07a49a22ce31fd1bfe266f29ff102305 100755
--- a/parallel_emerge
+++ b/parallel_emerge
@@ -310,13 +310,6 @@ class DepGraphGenerator(object):
       # will be going away soon as we migrate to CROS_WORKON_SRCROOT.
       os.environ.setdefault("CHROMEOS_ROOT", os.environ["HOME"] + "/trunk")
 
-      # Modify the environment to disable locking by default.
-      # TODO(davidjames): This option can cause problems if packages muck
-      # with each other during the post-install step. There are a few host
-      # packages that do this, so we only do this environment modification for
-      # board builds.
-      os.environ.setdefault("PORTAGE_LOCKS", "false")
-
     # Turn off interactive delays
     os.environ["EBEEP_IGNORE"] = "1"
     os.environ["EPAUSE_IGNORE"] = "1"
@@ -357,11 +350,17 @@ class DepGraphGenerator(object):
     # TODO(davidjames): Look for a better solution.
     features = os.environ.get("FEATURES", "") + " -collision-protect"
 
-    # If we're cross-compiling, updating the environment every time we install
-    # a package isn't necessary, and leads to race conditions when
-    # PORTAGE_LOCKS is false. In this case, do environment updates at the end,
-    # instead.
-    if self.board and os.environ.get("PORTAGE_LOCKS") == "false":
+    # If we're installing packages to the board, and we're not using the
+    # official flag, we can enable the following optimizations:
+    #  1) Don't lock during install step. This allows multiple packages to be
+    #     installed at once. This is safe because our board packages do not
+    #     muck with each other during the post-install step.
+    #  2) Don't update the environment until the end of the build. This is
+    #     safe because board packages don't need to run during the build --
+    #     they're cross-compiled, so our CPU architecture doesn't support them
+    #     anyway.
+    if self.board and os.environ.get("CHROMEOS_OFFICIAL") != "1":
+      os.environ.setdefault("PORTAGE_LOCKS", "false")
       features = features + " no-env-update"
 
     os.environ["FEATURES"] = features