Make gfx::Rect class operations consistently mutate the class they are called on.

ui/gfx/screen_gtk.cc

Index: ui/gfx/screen_gtk.cc
diff --git a/ui/gfx/screen_gtk.cc b/ui/gfx/screen_gtk.cc
index 7b0b34c8cd06dc4a51c0f396e2653b97dbd6a854..815864a1be20c08444c4a0230d630edfb8bd956b 100644
--- a/ui/gfx/screen_gtk.cc
+++ b/ui/gfx/screen_gtk.cc
@@ -141,7 +141,8 @@ gfx::Display Screen::GetPrimaryDisplay() {
   gfx::Display display(0, bounds);
   gfx::Rect rect;
   if (GetScreenWorkArea(&rect)) {
-    display.set_work_area(rect.Intersect(bounds));
+    rect.Intersect(bounds);
+    display.set_work_area(rect);
   } else {
     // Return the best we've got.
     display.set_work_area(bounds);