Add AshDesktopMediaList and enable Desktop Capture API on Chrome OS.

ui/snapshot/snapshot_win.cc

Index: ui/snapshot/snapshot_win.cc
diff --git a/ui/snapshot/snapshot_win.cc b/ui/snapshot/snapshot_win.cc
index 8c2ff3bd5bf93e8f003aa356c8f310967bd3cc1e..1d53ff45de5da299c5db1e84efeec0a80dc0eea6 100644
--- a/ui/snapshot/snapshot_win.cc
+++ b/ui/snapshot/snapshot_win.cc
@@ -103,6 +103,7 @@ bool GrabHwndSnapshot(HWND window_handle,
 }  // namespace internal
 
 #if !defined(USE_AURA)
+
 bool GrabViewSnapshot(gfx::NativeView view_handle,
                       std::vector<unsigned char>* png_representation,
                       const gfx::Rect& snapshot_bounds) {
@@ -116,6 +117,16 @@ bool GrabWindowSnapshot(gfx::NativeWindow window_handle,
   return internal::GrabHwndSnapshot(window_handle, snapshot_bounds,
                                     png_representation);
 }
+
+SNAPSHOT_EXPORT void GrapWindowSnapshotAsync(
+    gfx::NativeWindow window,
+    const gfx::Rect& snapshot_bounds,
+    const gfx::Size& target_size,
+    scoped_refptr<base::TaskRunner> background_task_runner,
+    GrapWindowSnapshotAsyncCallback callback) {
+  NOTIMPLEMENTED();
+}
+
 #endif  // !defined(USE_AURA)
 
 }  // namespace ui