Add context to gfx::Screen calls in support of simultaneous desktop+ash

ash/wm/workspace/frame_maximize_button.cc

Index: ash/wm/workspace/frame_maximize_button.cc
diff --git a/ash/wm/workspace/frame_maximize_button.cc b/ash/wm/workspace/frame_maximize_button.cc
index 697cc73c96689d2748442eac9a1e0517424eca33..76415d05738331cd4c6726d424ece968ed645f11 100644
--- a/ash/wm/workspace/frame_maximize_button.cc
+++ b/ash/wm/workspace/frame_maximize_button.cc
@@ -236,7 +236,7 @@ void FrameMaximizeButton::OnMouseExited(const ui::MouseEvent& event) {
   // within the bubble.
   if (!is_snap_enabled_ && maximizer_.get()) {
     if (maximizer_->GetBubbleWindow()) {
-      gfx::Point screen_location = gfx::Screen::GetCursorScreenPoint();
+      gfx::Point screen_location = Shell::GetScreen()->GetCursorScreenPoint();
       if (!maximizer_->GetBubbleWindow()->GetBoundsInScreen().Contains(
               screen_location)) {
         maximizer_.reset();
@@ -561,7 +561,7 @@ MaximizeBubbleFrameState
     return FRAME_STATE_FULL;
   // For Left/right maximize we need to check the dimensions.
   gfx::Rect bounds = frame_->GetWidget()->GetWindowBoundsInScreen();
-  gfx::Rect screen = gfx::Screen::GetDisplayMatching(bounds).work_area();
+  gfx::Rect screen = Shell::GetScreen()->GetDisplayMatching(bounds).work_area();
   if (bounds.width() < (screen.width() * kMinSnapSizePercent) / 100)
     return FRAME_STATE_NONE;
   // We might still have a horizontally filled window at this point which we