Make gtk2/gtk3 compile time switchable.

remoting/host/BUILD.gn

 # Copyright 2014 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")
 import("//build/config/ui.gni")
 import("//remoting/remoting_host.gni")
 import("//remoting/remoting_locales.gni")
 import("//remoting/remoting_srcs.gni")
 import("//remoting/remoting_version.gni")
@@ skipping 72 matching lines @@
     if (is_linux && !is_chromeos) {
       libs += [ "pam" ]
     }
 
     if (use_x11) {
       configs += [
         "//build/config/linux:x11",
         "//build/config/linux:xrandr",
       ]
       if (!is_chromeos) {
-        deps += [ "//build/config/linux/gtk" ]
+        deps += [ "//build/config/linux/gtk2" ]

[Nico, 2015/08/25 00:23:52]

same question

       }
     } else {
       sources -= [
         "clipboard_x11.cc",
         "desktop_resizer_x11.cc",
         "input_injector_x11.cc",
         "local_input_monitor_x11.cc",
       ]
       if (is_linux) {
         # These will already be filtered out on non-Linux.
@@ skipping 339 matching lines @@
         "//remoting/host",
         "//remoting/proto",
         "//third_party/webrtc/modules/desktop_capture",
       ]
 
       if (enable_webrtc) {
         deps += [ "//third_party/libjingle:libjingle_webrtc" ]
       }
 
       if (is_linux) {
-        deps += [ "//build/config/linux/gtk" ]
+        deps += [ "//build/config/linux/gtk2" ]
       }
       if (is_linux || is_mac) {
         libs = [ "pam" ]
       }
     }
 
     if (!is_win) {
       executable("remoting_me2me_host") {
         sources = [
           "host_main.cc",
           "host_main.h",
         ]
 
         deps = [
           ":remoting_me2me_host_static",
           ":credits",
         ]
       }
     }
   }
 }