[ios] Fix warning when running "gn gen".

ios/BUILD.gn

 # Copyright 2016 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.
 
 assert(!is_component_build, "component build is unsupported on iOS")
 
 import("//ios/features.gni")
 
 declare_args() {
   # TODO(brettw) bug 684096: Remove these. These are to prevent unused
   # override warnings on iOS from the setting of the default_args in the
   # toplevel //.gn file. Since iOS doesn't compile V8, GN complains that
   # the overrides are never used.
   v8_extra_library_files = []
   v8_experimental_extra_library_files = []
+  v8_enable_inspector = true
   v8_enable_gdbjit = false
   v8_imminent_deprecation_warnings = false
 }
 
 # Prevent warnings for unused build args above.
 assert(v8_extra_library_files != 0)
 assert(v8_experimental_extra_library_files != 0)
+assert(v8_enable_inspector)
 assert(!v8_enable_gdbjit)
 assert(!v8_imminent_deprecation_warnings)
 
 # This list all targets that needs to be build as part of "gn_all" on iOS.
 # This list should generally only include executables, but since some code
 # has not yet been upstreamed it will sometimes also include targets that
 # are not used upstream to ensure they are not broken inadvertently.
 group("all") {
   testonly = true
   if (is_cronet_build) {
@@ skipping 21 matching lines @@
       "//ios/clean/chrome/test:all_tests",
       "//ios/net:all_tests",
       "//ios/showcase:all_tests",
       "//ios/testing:all_tests",
       "//ios/web:all_tests",
       "//ios/web/shell/test:all_tests",
       "//ios/web_view/shell/test:all_tests",
     ]
   }
 }