Enable setting primary display for 3+ displays

ui/display/manager/display_layout.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/display/manager/display_layout.h"
 
 #include <algorithm>
 #include <set>
 #include <sstream>
 
@@ skipping 197 matching lines @@
                              const DisplayLayout& layout) {
   // The primary display should be in the list.
   DCHECK(IsIdInList(layout.primary_id, list));
 
   // Unified mode, or mirror mode switched from unified mode,
   // may not have the placement yet.
   if (layout.placement_list.size() == 0u)
     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;
     }
     if (placement.parent_display_id == kInvalidDisplayId) {
       LOG(ERROR) << "display_parent_id is not initialized";
       return false;
     }
     if (placement.display_id == placement.parent_display_id) {
       LOG(ERROR) << "display_id must not be same as parent_display_id";
@@ skipping 125 matching lines @@
 
   gfx::Insets insets = target_display->GetWorkAreaInsets();
   target_display->set_bounds(
       gfx::Rect(new_target_origin, target_bounds.size()));
   target_display->UpdateWorkAreaFromInsets(insets);
 
   return old_bounds != target_display->bounds();
 }
 
 }  // namespace display