Statically link own version of FreeType on Linux

build/config/freetype/BUILD.gn

 # Copyright 2017 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("//build/config/features.gni")
 
+declare_args() {
+  # Blink needs a recent and properly build-configured FreeType version to
+  # support OpenType variations, color emoji and avoid security bugs. By default
+  # We ship and link such a version as part of Chrome. For distributions that
+  # prefer to keep linking to the version the system, FreeType must be newer
+  # than version 2.7.1 and have color bitmap support compiled in. WARNING:
+  # System FreeType configurations other than as described WILL INTRODUCE TEXT
+  # RENDERING AND SECURITY REGRESSIONS.
+  use_system_freetype = false

[bungeman-chromium, 2017/05/05 20:59:54]

Should this (or its negation) be used in skia/BUILD.gn when deciding to define
SK_FREETYPE_MINIMUM_RUNTIME_VERSION ? Seems like that may simplify the logic
there and makes it more obvious what it's used for.

+}
+
 group("freetype") {
-  if (is_linux && !is_chromecast) {
+  if (is_chromeos || use_system_freetype) {

[Dirk Pranke, 2017/05/05 16:37:18]

Nit: is_chromeos does not mean this is an actual chromeos build, unfortunately.
We set target_os="chromeos" on the "desktop chromeos" builds as well, like 

https://luci-milo.appspot.com/buildbot/chromium.chromiumos/Linux%20ChromiumOS...

so this won't quite have the desired effect.

If you want a "true" chromeos build, you could check for `host_toolchain ==
"//build/toolchain/cros:host". However, it's probably better to just use
use_system_freetype and make sure they set the GN arg in their builds.

[vapier, 2017/05/05 17:50:51]

we should just update the Chrome OS ebuild to pass use_system_freetype=true, and
then we don't need this "is_chromeos" check at all

will GN reject unknown args ?  or is it safe to land that ebuild change now even
if the Chrome source doesn't check that arg ?

     public_configs = [ "//build/linux:freetype_from_pkgconfig" ]
   } else {
     public_deps = [
       "//third_party/freetype",
     ]
   }
 }