Makes ash/wm/common a library

ash/wm/aura/wm_globals_aura.cc

Index: ash/wm/aura/wm_globals_aura.cc
diff --git a/ash/wm/aura/wm_globals_aura.cc b/ash/wm/aura/wm_globals_aura.cc
index fe21613452368817d269796bb2ad27784955e3c8..c9c9d38eab303ca549b02f5006e02ff1991340c8 100644
--- a/ash/wm/aura/wm_globals_aura.cc
+++ b/ash/wm/aura/wm_globals_aura.cc
@@ -22,25 +22,14 @@
 
 namespace ash {
 namespace wm {
-namespace {
-
-WmGlobalsAura* instance_ = nullptr;
-
-}  // namespace
-
-// static
-WmGlobals* WmGlobals::Get() {
-  return instance_;
-}
 
 WmGlobalsAura::WmGlobalsAura() {
-  DCHECK(!instance_);
-  instance_ = this;
+  WmGlobals::Set(this);
   Shell::GetInstance()->AddShellObserver(this);
 }
 
 WmGlobalsAura::~WmGlobalsAura() {
-  instance_ = nullptr;
+  WmGlobals::Set(nullptr);
   if (added_activation_observer_) {
     aura::client::GetActivationClient(Shell::GetPrimaryRootWindow())
         ->RemoveObserver(this);
@@ -51,13 +40,6 @@ WmGlobalsAura::~WmGlobalsAura() {
   Shell::GetInstance()->RemoveShellObserver(this);
 }
 
-// static
-WmGlobalsAura* WmGlobalsAura::Get() {
-  if (!instance_)
-    new WmGlobalsAura;
-  return instance_;
-}
-
 WmWindow* WmGlobalsAura::GetFocusedWindow() {
   return WmWindowAura::Get(
       aura::client::GetFocusClient(Shell::GetPrimaryRootWindow())