Moves maintaining ShellObservers back to Shell

ash/accelerators/accelerator_interactive_uitest_chromeos.cc

Index: ash/accelerators/accelerator_interactive_uitest_chromeos.cc
diff --git a/ash/accelerators/accelerator_interactive_uitest_chromeos.cc b/ash/accelerators/accelerator_interactive_uitest_chromeos.cc
index 69755878e1647c2a25d64a9b1c32993a56993afb..274ca6efb3c01fb2efc29dd7769afe0f503eeea5 100644
--- a/ash/accelerators/accelerator_interactive_uitest_chromeos.cc
+++ b/ash/accelerators/accelerator_interactive_uitest_chromeos.cc
@@ -62,7 +62,7 @@ class AcceleratorInteractiveUITest : public AshInteractiveUITestBase,
   void SetUp() override {
     AshInteractiveUITestBase::SetUp();
 
-    WmShell::Get()->AddShellObserver(this);
+    Shell::GetInstance()->AddShellObserver(this);
 
     chromeos::NetworkHandler::Initialize();
   }
@@ -70,7 +70,7 @@ class AcceleratorInteractiveUITest : public AshInteractiveUITestBase,
   void TearDown() override {
     chromeos::NetworkHandler::Shutdown();
 
-    WmShell::Get()->RemoveShellObserver(this);
+    Shell::GetInstance()->RemoveShellObserver(this);
 
     AshInteractiveUITestBase::TearDown();
   }