Makes ash/wm/common a library

ash/wm/window_state_aura.cc

Index: ash/wm/window_state_aura.cc
diff --git a/ash/wm/window_state_aura.cc b/ash/wm/window_state_aura.cc
index 9bd2b3a993cd4a9538541dd85d9cdf696480c091..da677ae901ea45eb9eba19834d02cd958457d249 100644
--- a/ash/wm/window_state_aura.cc
+++ b/ash/wm/window_state_aura.cc
@@ -12,6 +12,18 @@
 
 namespace ash {
 namespace wm {
+namespace {
+
+class WindowStateAura : public wm::WindowState {

[James Cook, 2016/05/03 18:43:10]

Maybe comment on why this has to be here? At first look it's a little weird to
see a do-nothing wrapper class. I presume it's because wm::WindowState doesn't
want to have a public constructor, but has to be constructed outside the DLL?

[sky, 2016/05/03 19:10:06]

Yep. Added comment.

+ public:
+  explicit WindowStateAura(WmWindow* window) : wm::WindowState(window) {}
+  ~WindowStateAura() override {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(WindowStateAura);
+};
+
+}  // namespace
 
 WindowState* GetActiveWindowState() {
   aura::Window* active = GetActiveWindow();
@@ -23,7 +35,7 @@ WindowState* GetWindowState(aura::Window* window) {
     return nullptr;
   WindowState* settings = window->GetProperty(kWindowStateKey);
   if (!settings) {
-    settings = new WindowState(WmWindowAura::Get(window));
+    settings = new WindowStateAura(WmWindowAura::Get(window));
     window->SetProperty(kWindowStateKey, settings);
   }
   return settings;