GN: Fix Android component build

mojo/services/native_viewport/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/ui.gni")
 
 if (!is_android) {
   shared_library("native_viewport") {
     output_name = "mojo_native_viewport_service"
 
@@ skipping 45 matching lines @@
     "platform_viewport_android.cc",
     "platform_viewport_android.h",
     "platform_viewport_mac.mm",
     "platform_viewport_headless.cc",
     "platform_viewport_headless.h",
     "platform_viewport_win.cc",
     "viewport_surface.cc",
     "viewport_surface.h",
   ]
 
+  libs = []

[jamesr, 2014/10/22 00:28:19]

nit: you don't need this, although it'll be nice if more things are added

[cjhopman, 2014/10/23 00:15:48]

With this change (and previous ones), it's easier (slightly) to make
configuration-specific changes to targets that follow this pattern. I also like
that the stuff in the conditions is consistent in that it is modifying the
existing lists instead of assigning its own.

Also, to support two non-mutually-exclusive conditions that both add to libs
(or, more commonly deps), you need to define the list outside the conditions
(though it will just quietly work if you aren't in the configuration that hits
both conditions).

+
   if (is_ios) {
     sources += [ "platform_viewport_stub.cc" ]
   }
 
   if (is_android) {
     deps += [ "//mojo:jni_headers" ]
+    libs += [ "android" ]
   }
 
   if (use_x11) {
     sources += [ "platform_viewport_x11.cc" ]
     deps += [
       "//ui/events/platform/x11",
       "//ui/platform_window/x11",
     ]
   }
 
   if (use_ozone) {
     sources += [ "platform_viewport_ozone.cc" ]
   }
 }