Makes workspace 2 show an alternate background (system background)

ash/wm/workspace/workspace_manager2.cc

Index: ash/wm/workspace/workspace_manager2.cc
diff --git a/ash/wm/workspace/workspace_manager2.cc b/ash/wm/workspace/workspace_manager2.cc
index e57150eae99643487fb59e6400cee40e4d9278ef..897ce6c4bbe5d6eaeb5dfeede1a8fe0385602a74 100644
--- a/ash/wm/workspace/workspace_manager2.cc
+++ b/ash/wm/workspace/workspace_manager2.cc
@@ -18,6 +18,7 @@
 #include "ash/wm/window_animations.h"
 #include "ash/wm/window_properties.h"
 #include "ash/wm/window_util.h"
+#include "ash/wm/workspace/system_background_controller.h"
 #include "ash/wm/workspace/workspace_layout_manager2.h"
 #include "ash/wm/workspace/workspace2.h"
 #include "base/auto_reset.h"
@@ -265,6 +266,16 @@ void WorkspaceManager2::SetActiveWorkspace(Workspace2* workspace,
   Workspace2* last_active = active_workspace_;
   active_workspace_ = workspace;
 
+  destroy_background_timer_.Stop();
+  if (active_workspace_ == desktop_workspace()) {
+    destroy_background_timer_.Start(
+        FROM_HERE, GetSystemBackgroundDestroyDuration(),
+        this, &WorkspaceManager2::DestroySystemBackground);
+  } else if (!background_controller_.get()) {
+    background_controller_.reset(new SystemBackgroundController(
+                                     contents_view_->GetRootWindow()));
+  }
+
   UpdateShelfVisibility();
 
   if (animate_type != ANIMATE_NONE) {
@@ -368,6 +379,10 @@ void WorkspaceManager2::ScheduleDelete(Workspace2* workspace) {
                       &WorkspaceManager2::ProcessDeletion);
 }
 
+void WorkspaceManager2::DestroySystemBackground() {
+  background_controller_.reset();
+}
+
 void WorkspaceManager2::ProcessDeletion() {
   std::set<Workspace2*> to_delete;
   to_delete.swap(to_delete_);