Enable setting primary display for 3+ displays

ui/display/manager/display_layout.cc

Index: ui/display/manager/display_layout.cc
diff --git a/ui/display/manager/display_layout.cc b/ui/display/manager/display_layout.cc
index 25660de1af10c97f7f99a28c95d5557570c6a1ab..bfee319bd4d955b16f1b95234dd15bd3bc21e1ac 100644
--- a/ui/display/manager/display_layout.cc
+++ b/ui/display/manager/display_layout.cc
@@ -215,14 +215,14 @@ bool DisplayLayout::Validate(const DisplayIdList& list,
     return true;
 
   bool has_primary_as_parent = false;
-  int64_t id = 0;
-
+  int64_t prev_id = std::numeric_limits<int64_t>::min();
   for (const auto& placement : layout.placement_list) {
     // Placements are sorted by display_id.
-    if (id >= placement.display_id) {
+    if (prev_id >= placement.display_id) {
       LOG(ERROR) << "PlacementList must be sorted by display_id";
       return false;
     }
+    prev_id = placement.display_id;
     if (placement.display_id == kInvalidDisplayId) {
       LOG(ERROR) << "display_id is not initialized";
       return false;