Add remaining remoting targets for the GN build.

remoting/host/it2me/BUILD.gn

Index: remoting/host/it2me/BUILD.gn
diff --git a/remoting/host/it2me/BUILD.gn b/remoting/host/it2me/BUILD.gn
index 77dad430737e20393c2866862710335bdd252331..965977c3e73cfb55a392ed62ec86c67732f13211 100644
--- a/remoting/host/it2me/BUILD.gn
+++ b/remoting/host/it2me/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
+import("//remoting/remoting_host.gni")
 import("//remoting/remoting_srcs.gni")
 
 source_set("common") {
@@ -25,3 +26,33 @@ source_set("common") {
     "//remoting/resources",
   ]
 }
+
+if (!is_win && enable_remoting_host) {
+  executable("remote_assistance_host") {
+    sources = [
+      "it2me_native_messaging_host_entry_point.cc",
+      "it2me_native_messaging_host_main.cc",
+      "it2me_native_messaging_host_main.h",
+    ]
+
+    configs += [
+      "//build/config/compiler:wexit_time_destructors",
+      "//remoting:version",
+    ]
+
+    deps = [
+      ":common",
+      "//remoting/host",
+      "//remoting/host/native_messaging",
+      "//remoting/proto",
+    ]
+
+    if (enable_webrtc) {
+      deps += [ "//third_party/libjingle:libjingle_webrtc" ]
+    }
+
+    if (is_linux) {
+      deps += [ "//build/config/linux/gtk" ]
+    }
+  }
+}