Add a prototype today extension behind gn flag

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.
 
+import("//ios/build/chrome_build.gni")
+
 assert(!is_component_build, "component build is unsupported on iOS")
 
 declare_args() {
   # Control whether cronet is build (this is usually set by the script
   # components/cronet/tools/cr_cronet.py as cronet requires specific
   # gn args to build correctly).
   is_cronet_build = false
 }
 
 # This list all targets that needs to be build as part of "gn_all" on iOS.
@@ skipping 19 matching lines @@
 
       # List all the test targets that need to be build on iOS by default.
       "//ios/chrome/test:all_tests",
       "//ios/chrome/test/earl_grey:all_tests",
       "//ios/net:all_tests",
       "//ios/showcase:all_tests",
       "//ios/testing:all_tests",
       "//ios/web:all_tests",
       "//ios/web/shell/test:all_tests",
 
-      # Those dependencies are currently only used from downstream code
-      # and will be removed once the dependent code has been upstreamed.
+      # today_extension and share_extension dependencies are currently
+      # only used from downstream code and will be removed once the
+      # dependent code has been upstreamed.

[Olivier, 2017/01/17 10:13:05]

I think we can remove this.
Can you see with sdefresne?

[sdefresne, 2017/01/17 10:39:07]

Yes, just revert the whole file. I'll remove the dependency in a separate CL.

[lody, 2017/01/17 17:31:45]

Done.

       "//ios/chrome/share_extension",
-      "//ios/chrome/today_extension",
     ]
+    if (!ios_enable_today_extension && ios_enable_proto_today_extension) {

[Olivier, 2017/01/17 10:13:05]

This will add dep to today_extension if both flags are false.

[lody, 2017/01/17 17:31:45]

Acknowledged.

+      deps += [ "//ios/chrome/proto_today_extension" ]
+    } else {
+      deps += [ "//ios/chrome/today_extension" ]
+    }
   }
 }