platform-window: Add a PlatformWindowFactory for creating windows.

ui/platform_window/platform_window.gyp

Index: ui/platform_window/platform_window.gyp
diff --git a/ui/platform_window/platform_window.gyp b/ui/platform_window/platform_window.gyp
index 15162bfdf4560a18f3dbdfb9bdbd130bf42273e0..108f8c1123f33db4f9a270ab75920cb512921fd9 100644
--- a/ui/platform_window/platform_window.gyp
+++ b/ui/platform_window/platform_window.gyp
@@ -9,11 +9,16 @@
   'targets': [{
     'target_name': 'platform_window',
     'type': '<(component)',
+    'dependencies': [
+      '../../base/base.gyp:base',
+    ],
     'defines': [ 'PLATFORM_WINDOW_IMPLEMENTATION' ],
     'sources': [
       'platform_window.h',
       'platform_window_delegate.h',
       'platform_window_export.h',
+      'platform_window_factory.cc',
+      'platform_window_factory.h',
     ],
   }],
 }