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

ash/touch/touch_observer_hud.cc

Index: ash/touch/touch_observer_hud.cc
diff --git a/ash/touch/touch_observer_hud.cc b/ash/touch/touch_observer_hud.cc
index fb0aec27be85d3ebb552e4d66487cf390de78481..888678387219b217607d1067408964ddf86f49c8 100644
--- a/ash/touch/touch_observer_hud.cc
+++ b/ash/touch/touch_observer_hud.cc
@@ -42,7 +42,7 @@ class TouchHudCanvas : public views::View {
       : owner_(owner),
         path_index_(0),
         color_index_(0) {
-    gfx::Display display = gfx::Screen::GetPrimaryDisplay();
+    gfx::Display display = ash::Shell::GetAshScreen()->GetPrimaryDisplay();
     gfx::Rect bounds = display.bounds();
     size_.set_width(bounds.width() / kScale);
     size_.set_height(bounds.height() / kScale);