Improve WorkspaceWindowResizer::CompleteDrag() so that the function moves the window to a root windo

ash/test/ash_test_base.cc

Index: ash/test/ash_test_base.cc
diff --git a/ash/test/ash_test_base.cc b/ash/test/ash_test_base.cc
index 07f93d061b7ee077197e500eac5a45d6b040e157..e559833f26b13dd12124b64342372fd2f11f811a 100644
--- a/ash/test/ash_test_base.cc
+++ b/ash/test/ash_test_base.cc
@@ -7,6 +7,7 @@
 #include <string>
 #include <vector>
 
+#include "ash/display/display_controller.h"
 #include "ash/shell.h"
 #include "ash/test/test_shell_delegate.h"
 #include "base/run_loop.h"
@@ -87,6 +88,20 @@ void AshTestBase::UpdateDisplay(const std::string& display_specs) {
   std::vector<gfx::Display> displays = CreateDisplaysFromString(display_specs);
   aura::Env::GetInstance()->display_manager()->
       OnNativeDisplaysChanged(displays);
+
+  // On non-testing environment, when a secondary display is connected, a new
+  // native (i.e. X) window for the display is always created below the previous
+  // one for GPU performance reasons. Try to emulate the behavior.
+  if (internal::DisplayController::IsExtendedDesktopEnabled()) {
+    Shell::RootWindowList root_windows = Shell::GetAllRootWindows();
+    DCHECK_EQ(displays.size(), root_windows.size());
+    size_t next_y = 0;
+    for (size_t i = 0; i < root_windows.size(); ++i) {
+      const gfx::Size size = root_windows[i]->GetHostSize();
+      root_windows[i]->SetHostBounds(gfx::Rect(gfx::Point(0, next_y), size));
+      next_y += size.height();
+    }
+  }
 }
 
 void AshTestBase::RunAllPendingInMessageLoop() {