GN: Move configs for single-use Linux packages close to usage

Several configs in the Linux GN build are used in only one place.
Defining these configs in build/config/linux/BUILD.gn makes them
get resolved on all Linux-derived platforms, during both target
builds and host-tool builds. This doesn't work on CrOS, which
does not need or want the packages references by these configs.

gconf is used in multiple places, so moving the config won't work.
Instead, the gconf config is only resolved when building for
a Linux target.

BUG=None
TEST=GN build for Linux and CrOS
R=jamesr

Review URL: https://codereview.chromium.org/655343002

Cr-Commit-Position: refs/heads/master@{#299903}

build/config/linux/BUILD.gn

@@ -118,24 +118,16 @@ config("libresolv") {
 
 # CrOS doesn't install GTK, gconf or any gnome packages.
 if (!is_chromeos) {
-  pkg_config("gtk") {
-    # Gtk requires gmodule, but it does not list it as a dependency in some
-    # misconfigured systems.
-    packages = [ "gmodule-2.0", "gtk+-2.0", "gthread-2.0" ]
-  }
-
-  pkg_config("gtkprint") {
-    packages = [ "gtk+-unix-print-2.0" ]
-  }
-
-  pkg_config("gnome_keyring") {
-    packages = [ "gnome-keyring-1" ]
-  }
-
+  # These packages should _only_ be expected when building for a target.
+  # If these extra checks are not run, gconf is required when building host
+  # tools for a CrOS build.
+  if (current_toolchain == host_toolchain &&
+      host_toolchain == default_toolchain) {
     pkg_config("gconf") {
       packages = [ "gconf-2.0" ]
       defines = [ "USE_GCONF" ]
     }
+  }
 }
 
 # If brlapi isn't needed, don't require it to be installed.

chrome/browser/BUILD.gn

@@ -13,6 +13,9 @@ if (is_android) {
 } else {
   import("//tools/grit/grit_rule.gni")
 }
+if (is_desktop_linux) {
+  import("//build/config/linux/pkg_config.gni")
+}
 
 about_credits_file = "$target_gen_dir/about_credits.html"
 additional_modules_list_file =
@@ -24,6 +27,12 @@ gypi_values = exec_script(
     "scope",
     [ "../chrome_browser.gypi" ])
 
+if (is_desktop_linux) {
+  pkg_config("gnome_keyring") {
+    packages = [ "gnome-keyring-1" ]
+  }
+}
+
 static_library("browser") {
   configs += [
     "//build/config/compiler:wexit_time_destructors",
@@ -371,7 +380,7 @@ static_library("browser") {
   if (is_desktop_linux) {
     sources += rebase_path(gypi_values.chrome_browser_gnome_keyring_sources,
                            ".", "//chrome")
-    configs += [ "//build/config/linux:gnome_keyring" ]
+    configs += [ ":gnome_keyring" ]
   }
   if (use_aura) {
     sources += rebase_path(gypi_values.chrome_browser_aura_sources,

chrome/browser/ui/libgtk2ui/BUILD.gn

@@ -5,6 +5,17 @@
 assert(is_linux, "This file should only be referenced on Linux")
 
 import("//build/config/features.gni")
+import("//build/config/linux/pkg_config.gni")
+
+pkg_config("gtk") {
+  # Gtk requires gmodule, but it does not list it as a dependency in some
+  # misconfigured systems.
+  packages = [ "gmodule-2.0", "gtk+-2.0", "gthread-2.0" ]
+}
+
+pkg_config("gtkprint") {
+  packages = [ "gtk+-unix-print-2.0" ]
+}
 
 component("libgtk2ui") {
   sources = [
@@ -70,9 +81,9 @@ component("libgtk2ui") {
   defines = [ "LIBGTK2UI_IMPLEMENTATION" ]
 
   configs += [
+    ":gtk",
+    ":gtkprint",
     "//build/config/linux:gconf",
-    "//build/config/linux:gtk",
-    "//build/config/linux:gtkprint",
     "//printing:cups",
   ]