[iOS] Define global assert_no_deps and use it to prevent regressions.

ios/build/config.gni

Index: ios/build/config.gni
diff --git a/ios/build/config.gni b/ios/build/config.gni
new file mode 100644
index 0000000000000000000000000000000000000000..1f49440c10df61fd6eb65e2fc4a89b77ebee98dc
--- /dev/null
+++ b/ios/build/config.gni
@@ -0,0 +1,22 @@
+# 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.
+
+# Global list of dependencies that are conceptually bad on iOS and should
+# never be added (they will never be supported).
+conceptually_bad_dependencies = [

[brettw, 2016/03/18 21:17:50]

Can you call this ...ios_dependencies instead (same below)? When you import this
header, this will get into the namespace of the file and it won't be so clear.

Actually, it looks like maybe these aren't necessary outside of this header. If
that's the case, you can keep the names as-is and prefix then with _ to avoid
exporting them to BUILD files that import this.

[sdefresne, 2016/03/21 13:59:38]

Done (both changes).

+  "//cc/*",
+  "//content/*",
+  "//dbus/*",
+  "//ipc/*",
+  "//jingle/*",
+  "//media/*",
+  "//third_party/webrtc/*",
+  "//third_party/WebKit/*",
+]
+
+# Global list of conceptually fine dependencies but currently unsupported
+# on iOS. exclusions will be removed when the dependencies are fixed.
+transient_bad_dependencies = [ "//mojo/edk/*" ]
+
+ios_assert_no_deps = conceptually_bad_dependencies + transient_bad_dependencies