[GN] Add support for generating Xcode projects.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 284d1006aa6a8101e7f5e6c7b93e3dc1d9572636..af32dd769345e45f96cfcbf5299e93ce3e5293dc 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -225,6 +225,7 @@ group("both_gn_and_gyp") {
       "//ios/web:ios_web_inttests",
       "//ios/web:ios_web_unittests",
       "//ios/web/shell:ios_web_shell",
+      "//tools/gn(${host_toolchain})",

[sdefresne, 2016/04/27 17:41:53]

This is for convenience when working with iOS and on gn at the same time.

[brettw, 2016/04/27 23:09:30]

I think this makes it a bit confusing about what these lists of targets are for.
I usually find it easiest to build GN itself into a different output directory
than you're targeting anyway.

[sdefresne, 2016/04/28 09:29:12]

Ack, removed.

     ]
   }