Update from https://crrev.com/304121

build/config/linux/pkg_config.gni

Index: build/config/linux/pkg_config.gni
diff --git a/build/config/linux/pkg_config.gni b/build/config/linux/pkg_config.gni
index 378863e95510d08244dcebb27ccb4b9e527a84c7..687afc51c853ddf40dfb5390c1da19819eb894e7 100644
--- a/build/config/linux/pkg_config.gni
+++ b/build/config/linux/pkg_config.gni
@@ -33,25 +33,29 @@ declare_args() {
   pkg_config = ""
 }
 
+pkg_config_script = "//build/config/linux/pkg-config.py"
+
+# Define the args we pass to the pkg-config script for other build files that
+# need to invoke it manually.
+if (sysroot != "") {
+  # Pass the sysroot if we're using one (it requires the CPU arch also).
+  pkg_config_args = ["-s", sysroot, "-a", cpu_arch]
+} else if (pkg_config != "") {
+  pkg_config_args = ["-p", pkg_config]
+} else {
+  pkg_config_args = []
+}
+
 template("pkg_config") {
   assert(defined(invoker.packages),
         "Variable |packages| must be defined to be a list in pkg_config.")
   config(target_name) {
-    if (sysroot != "") {
-      # Pass the sysroot if we're using one (it requires the CPU arch also).
-      args = ["-s", sysroot, "-a", cpu_arch] + invoker.packages
-    } else if (pkg_config != "") {
-      args = ["-p", pkg_config] + invoker.packages
-    } else {
-      args = invoker.packages
-    }
-
+    args = pkg_config_args + invoker.packages
     if (defined(invoker.extra_args)) {
       args += invoker.extra_args
     }
 
-    pkgresult = exec_script("//build/config/linux/pkg-config.py",
-                            args, "value")
+    pkgresult = exec_script(pkg_config_script, args, "value")
     include_dirs = pkgresult[0]
     cflags = pkgresult[1]