Extract the code of showing a dragging window on another display from PhantomWindowController.

ash/wm/workspace/frame_maximize_button.cc

Index: ash/wm/workspace/frame_maximize_button.cc
diff --git a/ash/wm/workspace/frame_maximize_button.cc b/ash/wm/workspace/frame_maximize_button.cc
index 2d2a57a547397fec69a8c07697a72c446f8fbea3..81e89c4b10478166f09c48b38093286f22456085 100644
--- a/ash/wm/workspace/frame_maximize_button.cc
+++ b/ash/wm/workspace/frame_maximize_button.cc
@@ -385,7 +385,7 @@ void FrameMaximizeButton::UpdateSnap(const gfx::Point& location,
       snap_sizer_->Update(LocationForSnapSizer(location));
       phantom_window_->Show(ScreenAsh::ConvertRectToScreen(
           frame_->GetWidget()->GetNativeView()->parent(),
-          snap_sizer_->target_bounds()), NULL);
+          snap_sizer_->target_bounds()));
     }
     return;
   }
@@ -421,7 +421,7 @@ void FrameMaximizeButton::UpdateSnap(const gfx::Point& location,
     maximizer_->SetSnapType(snap_type_);
   }
   phantom_window_->Show(
-      ScreenBoundsForType(snap_type_, *snap_sizer_.get()), NULL);
+      ScreenBoundsForType(snap_type_, *snap_sizer_.get()));
 }
 
 SnapType FrameMaximizeButton::SnapTypeForLocation(