Rework how use_system_harfbuzz works a bit.

third_party/harfbuzz-ng/BUILD.gn

Index: third_party/harfbuzz-ng/BUILD.gn
diff --git a/third_party/harfbuzz-ng/BUILD.gn b/third_party/harfbuzz-ng/BUILD.gn
index 4824a4f864bfcb16e24cc7571d7bbef7be739726..81d4f65a9dafb5c15433af87c76ce0d782c06543 100644
--- a/third_party/harfbuzz-ng/BUILD.gn
+++ b/third_party/harfbuzz-ng/BUILD.gn
@@ -6,26 +6,13 @@ import("//build/config/chrome_build.gni")
 import("//build/config/linux/pkg_config.gni")
 import("//build/config/ui.gni")
 
-# The GYP build supports system harfbuzz for non-official builds when using
-# pangoft2 1.31.0 or greater (which pulls it in).
-# TODO(brettw) we can consider doing this as well, although the benefit is
-# unclear and requires shelling out to a script to check the version.
-#
-# ChromeOS uses an up-to-date system one that we have control over, so we
-# don't want to bloat the binary more by including another copy.
-
 declare_args() {
-  # Since version 1.31.0, pangoft2 which we depend on pulls in harfbuzz
-  # anyways. However, we want to have control of the version of harfbuzz
-  # we use, so don't use system harfbuzz unless we are building for
-  # chrome os, where we have the system harfbuzz under control.
-  use_system_harfbuzz =
-      is_linux && is_chromeos && exec_script(pkg_config_script,
-                                             pkg_config_args + [
-                                                   "--atleast-version=1.31.0",
-                                                   "pangoft2",
-                                                 ],
-                                             "value")
+  # Blink uses a cutting-edge version of Harfbuzz; most Linux distros do not

[Lei Zhang, 2016/04/06 23:35:08]

On Linux, we will hopefully bump the sysroot to Debian 8 or Ubuntu 14.04
sometime this year. Both distros have libpangoft2-1.0-0 1.36.x. Is that new
enough?

Maybe we can deprecate the pangoft hack targets then and assume this is always
true for Linux/ChromeOS.

+  # contain a new enough version of the code to work correctly. However,
+  # ChromeOS chroots (i.e, real ChromeOS builds for devices) do contain a
+  # new enough version of the library, and so this variable exists so that
+  # ChromeOS can build against the system lib and keep binary sizes smaller.
+  use_system_harfbuzz = false
 }
 
 if (use_system_harfbuzz) {