Push updates to inspector when windows are added, destroyed or reorganized

ash/common/devtools/ash_devtools_dom_agent.h

Index: ash/common/devtools/ash_devtools_dom_agent.h
diff --git a/ash/common/devtools/ash_devtools_dom_agent.h b/ash/common/devtools/ash_devtools_dom_agent.h
index 46af6a218063d135d0c3d4e5ccca6f04225711a0..760671f742105bb36dad4908993ab72fae3a4a7d 100644
--- a/ash/common/devtools/ash_devtools_dom_agent.h
+++ b/ash/common/devtools/ash_devtools_dom_agent.h
@@ -6,6 +6,7 @@
 #define ASH_COMMON_DEVTOOLS_ASH_DEVTOOLS_DOM_AGENT_H_
 
 #include "ash/common/wm_shell.h"
+#include "ash/common/wm_window_observer.h"
 #include "base/compiler_specific.h"
 #include "components/ui_devtools/DOM.h"
 #include "components/ui_devtools/devtools_base_agent.h"
@@ -15,22 +16,38 @@ namespace devtools {
 
 class ASH_EXPORT AshDevToolsDOMAgent
     : public NON_EXPORTED_BASE(ui::devtools::UiDevToolsBaseAgent<
-                               ui::devtools::protocol::DOM::Metainfo>) {
+                               ui::devtools::protocol::DOM::Metainfo>),
+      public WmWindowObserver {
  public:
   explicit AshDevToolsDOMAgent(ash::WmShell* shell);
   ~AshDevToolsDOMAgent() override;
 
   // DOM::Backend
-  ui::devtools::protocol::Response enable() override;
   ui::devtools::protocol::Response disable() override;
   ui::devtools::protocol::Response getDocument(
       std::unique_ptr<ui::devtools::protocol::DOM::Node>* out_root) override;
 
+  // WindowObserver
+  void OnWindowDestroying(WmWindow* window) override;
+  void OnWindowTreeChanged(WmWindow* window,
+                           const TreeChangeParams& params) override;
+  void OnWindowStackingChanged(WmWindow* window) override;
+
  private:
+  std::unique_ptr<ui::devtools::protocol::DOM::Node> BuildTreeForWindow(
+      WmWindow* window);
   std::unique_ptr<ui::devtools::protocol::DOM::Node> BuildInitialTree();
+  void AddWindowNode(WmWindow* window);
+  void RemoveWindowNode(WmWindow* window, WmWindow* old_parent);
+  void RemoveObserverFromAllWindows();
+  void AddRootWindowObservers();
+  void Reset();
 
   ash::WmShell* shell_;
 
+  using WindowToNodeIdMap = std::unordered_map<WmWindow*, int>;
+  WindowToNodeIdMap window_to_node_id_map_;
+
   DISALLOW_COPY_AND_ASSIGN(AshDevToolsDOMAgent);
 };