Export all CWV* symbols from the ios/web_view dynamic library.

ios/web_view/internal/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.
 
 source_set("internal") {
   visibility = [
     "//ios/web_view:*",
     "//ios/web_view/internal/*",
   ]
 
@@ skipping 23 matching lines @@
     "web_view_url_request_context_getter.mm",
     "web_view_web_client.h",
     "web_view_web_client.mm",
     "web_view_web_main_delegate.h",
     "web_view_web_main_delegate.mm",
     "web_view_web_main_parts.h",
     "web_view_web_main_parts.mm",
     "web_view_web_state_policy_decider.h",
     "web_view_web_state_policy_decider.mm",
   ]
+
+  # Let header files know that it is building ios/web_view library, not using
+  # it.
+  defines = [ "CWV_IMPLEMENTATION" ]
+
   deps = [
     "//base",
     "//components/pref_registry",
     "//components/prefs",
     "//components/translate/core/browser",
     "//components/translate/core/common",
     "//ios/net",
     "//ios/web",
     "//ios/web:reload_type",
     "//ios/web:user_agent",
     "//ios/web/public/app",
     "//ios/web_view/internal/translate",
     "//ios/web_view/public",
     "//net",
     "//net:extras",
     "//ui/base",
     "//url",
   ]
 
   allow_circular_includes_from = [ "//ios/web_view/internal/translate" ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
 }