Revert of gn BUILD fixes for disabling enable_extensions and use_ash feature flags.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index a98860f42d561e25d895e6c4fda562fe457a709b..35610ce68b48ff1294c3f9b1546440cb89a10afd 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -143,6 +143,8 @@
       "//chrome/test:interactive_ui_tests",
       "//chrome/test:sync_integration_tests",
       "//chrome/test/chromedriver:chromedriver_unittests",
+      "//extensions:extensions_browsertests",
+      "//extensions:extensions_unittests",
       "//gpu/gles2_conform_support:gles2_conform_test",
       "//gpu/khronos_glcts_support:khronos_glcts_test",
       "//jingle:jingle_unittests",
@@ -240,12 +242,7 @@
   deps += root_extra_deps
 
   if (enable_extensions) {
-    deps += [
-      "//extensions:extensions_browsertests",
-      "//extensions:extensions_unittests",
-      "//extensions/shell:app_shell",
-      "//extensions/shell:app_shell_unittests",
-    ]
+    deps += [ "//extensions/shell:app_shell_unittests" ]
   }
 
   if (enable_media_router) {
@@ -262,18 +259,14 @@
 
   if (use_aura) {
     deps += [
+      "//ash:ash_shell_with_content",
+      "//ash:ash_unittests",
       "//ui/app_list:app_list_unittests",
       "//ui/app_list/presenter:app_list_presenter_unittests",
       "//ui/aura:aura_unittests",
       "//ui/aura:demo",
       "//ui/wm:wm_unittests",
     ]
-    if (use_ash) {
-      deps += [
-        "//ash:ash_shell_with_content",
-        "//ash:ash_unittests",
-      ]
-    }
   }
 
   if (use_ozone) {
@@ -485,6 +478,10 @@
         "//third_party/leveldatabase:env_chromium_unittests",
         "//third_party/libaddressinput:libaddressinput_unittests",
       ]
+    }
+
+    if (enable_extensions) {
+      deps += [ "//extensions/shell:app_shell" ]
     }
 
     if (enable_nacl) {