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

ash/display/multi_display_manager.cc

Index: ash/display/multi_display_manager.cc
diff --git a/ash/display/multi_display_manager.cc b/ash/display/multi_display_manager.cc
index ef20b0e6302372e940877892eaa3e4adfd92e34a..02b6ee53f665040faeaf821bc3434d4befa568e7 100644
--- a/ash/display/multi_display_manager.cc
+++ b/ash/display/multi_display_manager.cc
@@ -311,7 +311,8 @@ const gfx::Display& MultiDisplayManager::GetDisplayMatching(
   for (std::vector<gfx::Display>::const_iterator iter = displays_.begin();
        iter != displays_.end(); ++iter) {
     const gfx::Display& display = *iter;
-    gfx::Rect intersect = display.bounds().Intersect(rect);
+    gfx::Rect intersect = display.bounds();
+    intersect.Intersect(rect);
     int area = intersect.width() * intersect.height();
     if (area > max) {
       max = area;