Remove the removed display from the active list after displays are added

ash/display/display_manager_unittest.cc

Index: ash/display/display_manager_unittest.cc
diff --git a/ash/display/display_manager_unittest.cc b/ash/display/display_manager_unittest.cc
index dfcd69a0a1e77c9618fe237a4c98fb3db4cc28df..fbb737cfdc97e4833a6fb8d8bc6cc27205bb913a 100644
--- a/ash/display/display_manager_unittest.cc
+++ b/ash/display/display_manager_unittest.cc
@@ -15,10 +15,12 @@
 #include "ash/test/ash_test_base.h"
 #include "ash/test/display_manager_test_api.h"
 #include "ash/test/mirror_window_test_api.h"
+#include "ash/wm/window_state.h"
 #include "base/command_line.h"
 #include "base/format_macros.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
+#include "ui/aura/client/aura_constants.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window_observer.h"
 #include "ui/aura/window_tree_host.h"
@@ -1512,6 +1514,27 @@ TEST_F(DisplayManagerTest, RotateUnifiedDesktop) {
   EXPECT_EQ("300x200", screen->GetPrimaryDisplay().size().ToString());
 }
 
+// Makes sure the transition from unified to single won't crash
+// with docked wnidows.
+TEST_F(DisplayManagerTest, UnifiedWithDockWindows) {
+  if (!SupportsMultipleDisplays())
+    return;
+
+  display_manager()->SetDefaultMultiDisplayMode(DisplayManager::UNIFIED);
+  display_manager()->SetMultiDisplayMode(DisplayManager::UNIFIED);
+  UpdateDisplay("300x200,400x500");
+
+  scoped_ptr<aura::Window> docked(
+      CreateTestWindowInShellWithBounds(gfx::Rect(10, 10, 50, 50)));
+  docked->SetProperty(aura::client::kShowStateKey, ui::SHOW_STATE_DOCKED);
+  ASSERT_TRUE(wm::GetWindowState(docked.get())->IsDocked());
+  EXPECT_EQ("0,0 250x453", docked->bounds().ToString());
+  UpdateDisplay("300x200");
+  // Make sure the window is still docked.
+  EXPECT_TRUE(wm::GetWindowState(docked.get())->IsDocked());
+  EXPECT_EQ("0,0 250x250", docked->bounds().ToString());
+}
+
 class ScreenShutdownTest : public test::AshTestBase {
  public:
   ScreenShutdownTest() {