platform-window: Add a PlatformWindowFactory for creating windows.

mojo/mojo_services.gypi

Index: mojo/mojo_services.gypi
diff --git a/mojo/mojo_services.gypi b/mojo/mojo_services.gypi
index 2384d4aa3d6bba21367367abb876fd064f051af8..19bfabb2d763d771fbbb701ceb99c807ff181753 100644
--- a/mojo/mojo_services.gypi
+++ b/mojo/mojo_services.gypi
@@ -311,12 +311,10 @@
         'services/native_viewport/native_viewport.h',
         'services/native_viewport/native_viewport_android.cc',
         'services/native_viewport/native_viewport_mac.mm',
-        'services/native_viewport/native_viewport_ozone.cc',
         'services/native_viewport/native_viewport_service.cc',
         'services/native_viewport/native_viewport_service.h',
         'services/native_viewport/native_viewport_stub.cc',
-        'services/native_viewport/native_viewport_win.cc',
-        'services/native_viewport/native_viewport_x11.cc',
+        'services/native_viewport/platform_viewport.cc',
       ],
       'conditions': [
         ['OS=="win" or OS=="android" or OS=="linux" or OS=="mac"', {
@@ -329,6 +327,15 @@
             'mojo_jni_headers',
           ],
         }],
+        ['use_x11==1 or use_ozone==1 or OS=="win"', {
+          'dependencies': [
+            '../ui/platform_window/platform_window.gyp:platform_window',
+          ],
+        }, {
+          'sources!': [
+            'services/native_viewport/platform_viewport.cc',
+          ],
+        }],
         ['OS=="win"', {
           'dependencies': [
             '../ui/platform_window/win/win_window.gyp:win_window',