Change GetAllDisplays() in all screens to return a const vector&.

ui/display/win/screen_win.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_DISPLAY_WIN_SCREEN_WIN_H_
 #define UI_DISPLAY_WIN_SCREEN_WIN_H_
 
 #include <windows.h>
 
 #include <memory>
@@ skipping 96 matching lines @@
 
   // Returns the NativeView associated with the HWND.
   virtual gfx::NativeWindow GetNativeWindowFromHWND(HWND hwnd) const;
 
  protected:
   // display::Screen:
   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;
+  const std::vector<display::Display>& GetAllDisplays() const override;
   display::Display GetDisplayNearestWindow(
       gfx::NativeView window) 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;
   gfx::Rect ScreenToDIPRectInWindow(
@@ skipping 50 matching lines @@
   void RecordDisplayScaleFactors() const;
 
   // Helper implementing the DisplayObserver handling.
   DisplayChangeNotifier change_notifier_;
 
   std::unique_ptr<gfx::SingletonHwndObserver> singleton_hwnd_observer_;
 
   // Current list of ScreenWinDisplays.
   std::vector<ScreenWinDisplay> screen_win_displays_;
 
+  // The display::Displays corresponding to |screen_win_displays_| for
+  // GetAllDisplays(). This must be updated anytime |screen_win_displays_| is
+  // updated.
+  std::vector<display::Display> displays_;
+
   DISALLOW_COPY_AND_ASSIGN(ScreenWin);
 };
 
 }  // namespace win
 }  // namespace display
 
 #endif  // UI_DISPLAY_WIN_SCREEN_WIN_H_