Move enable_app_list to a buildflag.

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 615 matching lines @@
 
       if (!is_debug && !is_component_build) {
         deps += [ "//chrome/tools/service_discovery_sniffer" ]
       }
 
       if (is_clang) {
         deps += [ "//build/sanitizers:copy_llvm_symbolizer" ]
       }
     }
 
-    if (enable_app_list) {
-      deps += [ "//ui/app_list:app_list_demo" ]
-    }
-
     if (use_x11) {
       if (target_cpu != "arm") {
         deps += [ "//gpu/tools/compositor_model_bench" ]
       }
     }
   }
 
   if (is_mac) {
     deps += [
       "//breakpad:crash_inspector",
@@ skipping 507 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",
     ]
   }
 }