gfx: Make conversions from Size to SizeF be explicit.

ash/display/display_manager.cc

Index: ash/display/display_manager.cc
diff --git a/ash/display/display_manager.cc b/ash/display/display_manager.cc
index 045f3a9500aeec67bac889f70e188d1a1caf498e..e4643208c3ecf49d54c5c7c66a793e6a7acc9523 100644
--- a/ash/display/display_manager.cc
+++ b/ash/display/display_manager.cc
@@ -1299,8 +1299,8 @@ gfx::Display DisplayManager::CreateMirroringDisplayFromDisplayInfoById(
 
   gfx::Display new_display(display_info.id());
   new_display.SetScaleAndBounds(
-      1.0f, gfx::Rect(origin, gfx::ToFlooredSize(gfx::ScaleSize(
-                                  display_info.size_in_pixel(), scale))));
+      1.0f, gfx::Rect(origin, gfx::ScaleToFlooredSize(
+                                  display_info.size_in_pixel(), scale)));
   new_display.set_touch_support(display_info.touch_support());
   return new_display;
 }