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

ui/display/win/screen_win.h

Index: ui/display/win/screen_win.h
diff --git a/ui/display/win/screen_win.h b/ui/display/win/screen_win.h
index 422077d521282c11243eb15cb2a9a58e45f6f2fa..a559013c1bcc9f3317e3058e7013c9f996650ad7 100644
--- a/ui/display/win/screen_win.h
+++ b/ui/display/win/screen_win.h
@@ -114,7 +114,7 @@ class DISPLAY_EXPORT ScreenWin : public display::Screen {
   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(
@@ -184,6 +184,8 @@ class DISPLAY_EXPORT ScreenWin : public display::Screen {
 
   // Current list of ScreenWinDisplays.
   std::vector<ScreenWinDisplay> screen_win_displays_;
+  // The corresponding display::Display.

[robliao, 2016/11/12 00:11:06]

Nit: Linebreak above and use this as the comment "The display::Displays
corresponding to |screen_win_displays_| for GetAllDisplays(). This must be
updated anytime |screen_win_displays_| is updated."

[riajiang, 2016/11/15 20:08:13]

Done.

+  std::vector<display::Display> displays_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenWin);
 };