Move DisplayList to display; add ScreenBase.

ui/display/screen_base.h

Index: ui/display/screen_base.h
diff --git a/ash/mus/test/wm_test_screen.h b/ui/display/screen_base.h
similarity index 54%
copy from ash/mus/test/wm_test_screen.h
copy to ui/display/screen_base.h
index 4545804432cde15ca228e7a0671d05aed92744cc..e0c5b1c2ecf96b63c800be5a1e638b79dcaad57e 100644
--- a/ash/mus/test/wm_test_screen.h
+++ b/ui/display/screen_base.h
@@ -2,24 +2,29 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef ASH_MUS_TEST_WM_TEST_SCREEN_H_
-#define ASH_MUS_TEST_WM_TEST_SCREEN_H_
+#ifndef UI_DISPLAY_SCREEN_BASE_H_
+#define UI_DISPLAY_SCREEN_BASE_H_
 
+#include "ui/display/display.h"
+#include "ui/display/display_export.h"
+#include "ui/display/display_list.h"
 #include "ui/display/screen.h"
-#include "ui/views/mus/display_list.h"
 
-namespace ash {
-namespace mus {
+namespace display {
 
-// Screen implementation used by tests for the windowmanager. Does not talk
-// to mus. Tests must keep the list of Displays in sync manually.
-class WmTestScreen : public display::Screen {
+// Simple screen implementation with a display list.
+class DISPLAY_EXPORT ScreenBase : public display::Screen {
  public:
-  WmTestScreen();
-  ~WmTestScreen() override;
+  ScreenBase();
+  ~ScreenBase() override;
 
-  const views::DisplayList& display_list() const { return display_list_; }
-  views::DisplayList* display_list() { return &display_list_; }
+  display::DisplayList* display_list() { return &display_list_; };
+
+ protected:
+  // Invoked when a display changed in some way, including being added.
+  // If |is_primary| is true, |changed_display| is the primary display.
+  void ProcessDisplayChanged(const display::Display& changed_display,
+                             bool is_primary);
 
  private:
   // display::Screen:
@@ -37,12 +42,11 @@ class WmTestScreen : public display::Screen {
   void AddObserver(display::DisplayObserver* observer) override;
   void RemoveObserver(display::DisplayObserver* observer) override;
 
-  views::DisplayList display_list_;
+  display::DisplayList display_list_;
 
-  DISALLOW_COPY_AND_ASSIGN(WmTestScreen);
+  DISALLOW_COPY_AND_ASSIGN(ScreenBase);
 };
 
-}  // namespace mus
-}  // namespace ash
+}  // namespace display
 
-#endif  // ASH_MUS_TEST_WM_TEST_SCREEN_H_
+#endif  // UI_DISPLAY_SCREEN_BASE_H_