Converts DockedWindowLayoutManager to common ash/wm types

ash/wm/dock/docked_window_layout_manager_unittest.cc

Index: ash/wm/dock/docked_window_layout_manager_unittest.cc
diff --git a/ash/wm/dock/docked_window_layout_manager_unittest.cc b/ash/wm/dock/docked_window_layout_manager_unittest.cc
index 57869196d4e70f4d78fdb1ee8496d11c8f142ba7..3f629b359de865d037d47d5988377a6f6aa6b493 100644
--- a/ash/wm/dock/docked_window_layout_manager_unittest.cc
+++ b/ash/wm/dock/docked_window_layout_manager_unittest.cc
@@ -270,8 +270,8 @@ TEST_P(DockedWindowLayoutManagerTest, AutoPlacingLeft) {
             window->GetBoundsInScreen().x());
   EXPECT_EQ(kShellWindowId_DockedContainer, window->parent()->id());
 
-  DockedWindowLayoutManager* manager = static_cast<DockedWindowLayoutManager*>(
-      window->parent()->layout_manager());
+  DockedWindowLayoutManager* manager =
+      DockedWindowLayoutManager::Get(wm::WmWindowAura::Get(window.get()));
 
   // Create two additional windows and test their auto-placement
   std::unique_ptr<aura::Window> window1(CreateTestWindowInShellWithId(1));
@@ -320,8 +320,8 @@ TEST_P(DockedWindowLayoutManagerTest, AutoPlacingRight) {
             window->GetBoundsInScreen().right());
   EXPECT_EQ(kShellWindowId_DockedContainer, window->parent()->id());
 
-  DockedWindowLayoutManager* manager = static_cast<DockedWindowLayoutManager*>(
-      window->parent()->layout_manager());
+  DockedWindowLayoutManager* manager =
+      DockedWindowLayoutManager::Get(wm::WmWindowAura::Get(window.get()));
 
   // Create two additional windows and test their auto-placement
   std::unique_ptr<aura::Window> window1(CreateTestWindowInShellWithId(1));
@@ -374,8 +374,8 @@ TEST_P(DockedWindowLayoutManagerTest, AutoPlacingRightSecondScreen) {
             window->GetBoundsInScreen().right());
   EXPECT_EQ(kShellWindowId_DockedContainer, window->parent()->id());
 
-  DockedWindowLayoutManager* manager = static_cast<DockedWindowLayoutManager*>(
-      window->parent()->layout_manager());
+  DockedWindowLayoutManager* manager =
+      DockedWindowLayoutManager::Get(wm::WmWindowAura::Get(window.get()));
 
   // Create two additional windows and test their auto-placement
   bounds = gfx::Rect(616, 32, 231, 320);