Add ui::GrabDesktopSnapshot for Windows.

ui/snapshot/snapshot.gyp

Index: ui/snapshot/snapshot.gyp
diff --git a/ui/snapshot/snapshot.gyp b/ui/snapshot/snapshot.gyp
index 40744bfc768359129ecd467b2a9810dace3d3aeb..cf93fa9366c2dc81ae5639188b6a5123f6a293c8 100644
--- a/ui/snapshot/snapshot.gyp
+++ b/ui/snapshot/snapshot.gyp
@@ -27,6 +27,7 @@
         'snapshot_ios.mm',
         'snapshot_mac.mm',
         'snapshot_win.cc',
+        'snapshot_win.h',
       ],
       'include_dirs': [
         '..',
@@ -38,11 +39,6 @@
             '../compositor/compositor.gyp:compositor',
           ],
         }],
-        ['use_aura==1 and OS=="win"', {
-          'sources/': [
-            ['exclude', 'snapshot_win.cc'],
-          ],
-        }],
       ],
     },
     {
@@ -62,4 +58,24 @@
       ]
     },
   ],
+  'conditions': [
+    ['OS=="win"', {
+      'targets': [
+        {
+          'target_name': 'snapshot_test_support',
+          'type': 'static_library',
+          'sources': [
+            'test/snapshot_desktop.h',
+            'test/snapshot_desktop_win.cc',
+          ],
+          'dependencies': [
+            'snapshot',
+          ],
+          'include_dirs': [
+            '../..',
+          ],
+        },
+      ],
+    }],
+  ],
 }