Make gfx::Display Final

gfx::Display is designed to be copied, so no one should inherit from
gfx::Display.

BUG=426656

Review URL: https://codereview.chromium.org/1614953003

Cr-Commit-Position: refs/heads/master@{#370774}

ui/gfx/display.h

@@ -21,7 +21,7 @@ namespace gfx {
 // system. For platforms that support DIP (density independent pixel),
 // |bounds()| and |work_area| will return values in DIP coordinate
 // system, not in backing pixels.
-class GFX_EXPORT Display {
+class GFX_EXPORT Display final {
  public:
   // Screen Rotation in clock-wise degrees.
   // This enum corresponds to DisplayRotationDefaultProto::Rotation in