Improve doc of ViewObserver and clarify arguments

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 97990430c5b8c922b2d037f183a89da3a4af30a2..758bf63c251f34ca0e82ae283b8e2a5e59b8ce86 100644
--- a/ash/common/devtools/ash_devtools_dom_agent.h
+++ b/ash/common/devtools/ash_devtools_dom_agent.h
@@ -67,9 +67,9 @@ class ASH_EXPORT AshDevToolsDOMAgent
                              const gfx::Rect& new_bounds) override;
 
   // views::ViewObserver
-  void OnChildViewRemoved(views::View* view, views::View* parent) override;
-  void OnChildViewAdded(views::View* view) override;
-  void OnChildViewReordered(views::View*) override;
+  void OnChildViewRemoved(views::View* parent, views::View* view) override;
+  void OnChildViewAdded(views::View* parent, views::View* view) override;
+  void OnChildViewReordered(views::View* parent, views::View*) override;
   void OnViewBoundsChanged(views::View* view) override;
 
   WmWindow* GetWindowFromNodeId(int nodeId);