ui: Cleanup class/struct forward declarations

extensions/shell/browser/shell_screen.h

Index: extensions/shell/browser/shell_screen.h
diff --git a/extensions/shell/browser/shell_screen.h b/extensions/shell/browser/shell_screen.h
index fed63dfd58f1d7be4bb60a19fe73b5e60d6ec1d6..866a36ee2cdb26e1607f2e2d6d03b9e2a4c113eb 100644
--- a/extensions/shell/browser/shell_screen.h
+++ b/extensions/shell/browser/shell_screen.h
@@ -8,7 +8,7 @@
 #include "base/macros.h"
 #include "ui/aura/window_observer.h"
 #include "ui/display/display.h"
-#include "ui/display/screen.h"
+#include "ui/display/screen_base.h"
 
 namespace aura {
 class WindowTreeHost;
@@ -22,7 +22,7 @@ namespace extensions {
 
 // A minimal Aura implementation of a screen. Scale factor is locked at 1.0.
 // When running on a Linux desktop resizing the main window resizes the screen.
-class ShellScreen : public display::Screen, public aura::WindowObserver {
+class ShellScreen : public display::ScreenBase, public aura::WindowObserver {
  public:
   // Creates a screen occupying |size| physical pixels.
   explicit ShellScreen(const gfx::Size& size);
@@ -41,20 +41,10 @@ class ShellScreen : public display::Screen, public aura::WindowObserver {
   gfx::Point GetCursorScreenPoint() override;
   bool IsWindowUnderCursor(gfx::NativeWindow window) override;
   gfx::NativeWindow GetWindowAtScreenPoint(const gfx::Point& point) override;
-  int GetNumDisplays() const override;
-  std::vector<display::Display> GetAllDisplays() const override;
   display::Display GetDisplayNearestWindow(gfx::NativeView view) const override;
-  display::Display GetDisplayNearestPoint(
-      const gfx::Point& point) const override;
-  display::Display GetDisplayMatching(
-      const gfx::Rect& match_rect) const override;
-  display::Display GetPrimaryDisplay() const override;
-  void AddObserver(display::DisplayObserver* observer) override;
-  void RemoveObserver(display::DisplayObserver* observer) override;
 
  private:
   aura::WindowTreeHost* host_;  // Not owned.
-  display::Display display_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellScreen);
 };