Fix expected PlacementList sort order.

ui/display/display_layout_unittest.cc

Index: ui/display/display_layout_unittest.cc
diff --git a/ui/display/display_layout_unittest.cc b/ui/display/display_layout_unittest.cc
index d5abf695cda1bd5d51098ea1a7bb2af3cc2df66f..a367c003dbcd0af4edcf9bad3346b5a507ddd249 100644
--- a/ui/display/display_layout_unittest.cc
+++ b/ui/display/display_layout_unittest.cc
@@ -91,14 +91,15 @@ TEST(DisplayLayoutTest, SwapPrimaryDisplayThreeDisplays) {
           .AddDisplayPlacement(789, 456, Position::RIGHT, 0)
           .Build();
 
-  // Initial layout will be 123 --> 456 <-- 789.
+  // Note: Placement order is determined by least significant 8 bits of IDs.
+  // Initial layout will be 123 (0x7B) --> 456 (0x1C8) <-- 789 (0x315).
   EXPECT_EQ(456, layout->primary_id);
-  EXPECT_EQ(123, layout->placement_list[0].display_id);
+  EXPECT_EQ(789, layout->placement_list[0].display_id);
   EXPECT_EQ(456, layout->placement_list[0].parent_display_id);
-  EXPECT_EQ(Position::LEFT, layout->placement_list[0].position);
-  EXPECT_EQ(789, layout->placement_list[1].display_id);
+  EXPECT_EQ(Position::RIGHT, layout->placement_list[0].position);
+  EXPECT_EQ(123, layout->placement_list[1].display_id);
   EXPECT_EQ(456, layout->placement_list[1].parent_display_id);
-  EXPECT_EQ(Position::RIGHT, layout->placement_list[1].position);
+  EXPECT_EQ(Position::LEFT, layout->placement_list[1].position);
 
   // Swap layout to 123 --> 456 --> 789.
   layout->SwapPrimaryDisplay(789);
@@ -113,14 +114,40 @@ TEST(DisplayLayoutTest, SwapPrimaryDisplayThreeDisplays) {
   // Swap layout to 123 <-- 456 <-- 789.
   layout->SwapPrimaryDisplay(123);
   EXPECT_EQ(123, layout->primary_id);
-  EXPECT_EQ(456, layout->placement_list[0].display_id);
-  EXPECT_EQ(123, layout->placement_list[0].parent_display_id);
+  EXPECT_EQ(789, layout->placement_list[0].display_id);
+  EXPECT_EQ(456, layout->placement_list[0].parent_display_id);
   EXPECT_EQ(Position::RIGHT, layout->placement_list[0].position);
-  EXPECT_EQ(789, layout->placement_list[1].display_id);
-  EXPECT_EQ(456, layout->placement_list[1].parent_display_id);
+  EXPECT_EQ(456, layout->placement_list[1].display_id);
+  EXPECT_EQ(123, layout->placement_list[1].parent_display_id);
   EXPECT_EQ(Position::RIGHT, layout->placement_list[1].position);
 }
 
+// Makes sure that only the least significant 8 bits of the display IDs in the
+// placement lists are used to validate their sort order.
+TEST(DisplayLayoutTest, PlacementSortOrder) {
+  // Sorted placement lists by full IDs, but not sorted by the least significant
+  // 8 bits of the IDs.
+  std::unique_ptr<DisplayLayout> layout(new DisplayLayout);
+  layout->primary_id = 456;
+  layout->placement_list.emplace_back(0x0405, 456, Position::LEFT, 0,
+                                      DisplayPlacement::TOP_LEFT);
+  layout->placement_list.emplace_back(0x0506, 0x0405, Position::RIGHT, 0,
+                                      DisplayPlacement::TOP_LEFT);
+  layout->placement_list.emplace_back(0x0604, 0x0506, Position::RIGHT, 0,
+                                      DisplayPlacement::TOP_LEFT);
+  EXPECT_FALSE(DisplayLayout::Validate({456, 0x0405, 0x0506, 0x0604}, *layout));
+
+  // Full IDs not sorted, but least significant 8 bits of the IDs are sorted.
+  layout->placement_list.clear();
+  layout->placement_list.emplace_back(0x0504, 456, Position::LEFT, 0,
+                                      DisplayPlacement::TOP_LEFT);
+  layout->placement_list.emplace_back(0x0605, 0x0504, Position::RIGHT, 0,
+                                      DisplayPlacement::TOP_LEFT);
+  layout->placement_list.emplace_back(0x0406, 0x0605, Position::RIGHT, 0,
+                                      DisplayPlacement::TOP_LEFT);
+  EXPECT_TRUE(DisplayLayout::Validate({456, 0x0504, 0x0605, 0x0406}, *layout));
+}
+
 namespace {
 
 class TwoDisplays