Make gtk2/gtk3 compile time switchable.

build/config/linux/gtk3/BUILD.gn

Index: build/config/linux/gtk3/BUILD.gn
diff --git a/build/config/linux/gtk/BUILD.gn b/build/config/linux/gtk3/BUILD.gn
similarity index 77%
rename from build/config/linux/gtk/BUILD.gn
rename to build/config/linux/gtk3/BUILD.gn
index 9c9c696fcf38394744e6f16bee09d66ca20d9a7d..b61ef94b1be5867155e5194afc4be2bd353b65e6 100644
--- a/build/config/linux/gtk/BUILD.gn
+++ b/build/config/linux/gtk3/BUILD.gn
@@ -6,24 +6,24 @@ import("//build/config/linux/pkg_config.gni")
 
 assert(is_linux, "This file should only be referenced on Linux")
 
-# Depend on //build/config/linux/gtk to use GTK.
+# Depend on //build/config/linux/gtk3 to use GTKv3.
 #
 # GN doesn't check visibility for configs so we give this an obviously internal
 # name to discourage random targets from accidentally depending on this and
 # bypassing the GTK target's visibility.
-pkg_config("gtk_internal_config") {
+pkg_config("gtk3_internal_config") {
   # Gtk requires gmodule, but it does not list it as a dependency in some
   # misconfigured systems.
   packages = [
     "gmodule-2.0",
-    "gtk+-2.0",
+    "gtk+-3.0",
     "gthread-2.0",
   ]
 }
 
 # Basically no parts of Chrome should depend on GTK. To prevent accidents, the
 # parts that explicitly need GTK are whitelisted on this target.
-group("gtk") {
+group("gtk3") {
   visibility = [
     "//chrome/browser/ui/libgtk2ui",
     "//gpu/gles2_conform_support:gles2_conform_test_windowless",
@@ -31,15 +31,15 @@ group("gtk") {
     "//remoting/host/it2me:remote_assistance_host",
     "//remoting/host:remoting_me2me_host_static",
   ]
-  public_configs = [ ":gtk_internal_config" ]
+  public_configs = [ ":gtk3_internal_config" ]
 }
 
 # Depend on "gtkprint" to get this.
-pkg_config("gtkprint_internal_config") {
-  packages = [ "gtk+-unix-print-2.0" ]
+pkg_config("gtkprint3_internal_config") {
+  packages = [ "gtk+-unix-print-3.0" ]
 }
 
-group("gtkprint") {
+group("gtkprint3") {
   visibility = [ "//chrome/browser/ui/libgtk2ui" ]
-  public_configs = [ ":gtkprint_internal_config" ]
+  public_configs = [ ":gtkprint3_internal_config" ]
 }