Refactor screen/monitor so that gfx::Screen returns monitor object.

ui/ui.gyp

Index: ui/ui.gyp
diff --git a/ui/ui.gyp b/ui/ui.gyp
index 61cf11020e300bc4990a1e4632db2a1e500d2154..9bb6d56261848c80008d0ade90dad73259f97d5b 100644
--- a/ui/ui.gyp
+++ b/ui/ui.gyp
@@ -317,6 +317,10 @@
         'gfx/mac/nsimage_cache.h',
         'gfx/mac/nsimage_cache.mm',
         'gfx/mac/scoped_ns_disable_screen_updates.h',
+        'gfx/monitor.cc',
+        'gfx/monitor.h',
+        'gfx/monitor_observer.cc',
+        'gfx/monitor_observer.h',
         'gfx/native_theme.cc',
         'gfx/native_theme.h',
         'gfx/native_theme_android.cc',
@@ -358,10 +362,12 @@
         'gfx/render_text_linux.h',
         'gfx/render_text_win.cc',
         'gfx/render_text_win.h',
+        'gfx/screen.cc',
         'gfx/screen.h',
         'gfx/screen_android.cc',
-        'gfx/screen_ash.cc',
+        'gfx/screen_aura.cc',
         'gfx/screen_gtk.cc',
+        'gfx/screen_impl.h',
         'gfx/screen_mac.mm',
         'gfx/screen_win.cc',
         'gfx/scoped_cg_context_save_gstate_mac.h',