Change 'chromium_builder_tests' to be empty in GN 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 67 matching lines @@
 # for the iOS bots and the official builders.
 group("All") {
   testonly = true
 
   deps = [
     ":gn_all",
   ]
 }
 
 # TODO(GYP_GONE): This target exists for compatibility with GYP for the
-# builders. For now, this builds everything. We should decide if we want to
-# build less.
+# builders that specify targets in the recipes directly.
+# Ideally it should not exist, and the builders should be specifying
+# more specific targets (or 'All') via the source-side
+# //testing/buildbot/*.json files. We should simply delete this target
+# and update any recipes that are using it.
 group("chromium_builder_tests") {
   testonly = true
-
-  deps = [
-    ":All",
-  ]
+  deps = []
 }
 
 if (is_chromeos) {
   group("chromiumos_preflight") {
     testonly = true
     deps = [
       "//breakpad:minidump_stackwalk($host_toolchain)",
       "//chrome",
       "//chrome/test/chromedriver",
       "//media:media_unittests",
@@ skipping 884 matching lines @@
   assert(target_name != "")  # Mark as used.
   sources = invoker.actual_sources
   assert(
       sources == invoker.actual_sources,
       "Do not use a platform name in your output directory (found \"$root_build_dir\"). http://crbug.com/548283")
 }
 
 assert_valid_out_dir("_unused") {
   actual_sources = [ "$root_build_dir/foo" ]
 }