Don't allow official component builds

BUILD.gn

 # Copyright (c) 2013 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.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 12 matching lines @@
   import("//build/config/android/config.gni")
 }
 
 declare_args() {
   # A list of extra dependencies to add to the root target. This allows a
   # checkout to add additional targets without explicitly changing any checked-
   # in files.
   root_extra_deps = []
 }
 
+if (is_official_build) {
+  # An official (maximally optimized!) component (optimized for build times)
+  # build doesn't make sense and usually doesn't work.
+  assert(!is_component_build)
+}
+
 # This file defines the following five main targets:
 #
 # "both_gn_and_gyp" should list every root target (target that nothing else
 # depends on) built by GN that is also built in the GYP build.
 #
 # "gn_all" should (transitively) cause everything to be built; if you run
 # 'ninja gn_all' and then 'ninja all', the second build should do no work.
 #
 # "gn_only" should list every root target that is *not* intended to be built in
 # a GYP build. Because GN has different rules for deciding what an 'all' build
@@ skipping 1083 matching lines @@
       "//ui/display:display_unittests",
       "//ui/events:events_unittests",
       "//ui/gfx:gfx_unittests",
       "//ui/gl:gl_unittests",
       "//ui/keyboard:keyboard_unittests",
       "//ui/touch_selection:ui_touch_selection_unittests",
       "//url:url_unittests",
     ]
   }
 }