Create a unified UIElement interface for Widget, View and Window.

ash/common/devtools/ash_devtools_css_agent.h

Index: ash/common/devtools/ash_devtools_css_agent.h
diff --git a/ash/common/devtools/ash_devtools_css_agent.h b/ash/common/devtools/ash_devtools_css_agent.h
index e83fdfbeaf6e4e9f51bd479ea1e4372d11fb5c8c..e15a3b447bd65f9801f0bbcf08459f50ce544ce3 100644
--- a/ash/common/devtools/ash_devtools_css_agent.h
+++ b/ash/common/devtools/ash_devtools_css_agent.h
@@ -5,7 +5,9 @@
 #ifndef ASH_COMMON_DEVTOOLS_ASH_DEVTOOLS_CSS_AGENT_H_
 #define ASH_COMMON_DEVTOOLS_ASH_DEVTOOLS_CSS_AGENT_H_
 
+#include "ash/ash_export.h"
 #include "ash/common/devtools/ash_devtools_dom_agent.h"
+#include "ash/common/devtools/ui_element.h"
 #include "components/ui_devtools/CSS.h"
 #include "ui/views/widget/widget_observer.h"
 
@@ -35,9 +37,7 @@ class ASH_EXPORT AshDevToolsCSSAgent
           result) override;
 
   // AshDevToolsDOMAgentObserver
-  void OnWindowBoundsChanged(WmWindow* window) override;
-  void OnWidgetBoundsChanged(views::Widget* widget) override;
-  void OnViewBoundsChanged(views::View* view) override;
+  void OnUIElementBoundsChanged(UIElement* ui_element) override;
 
  private:
   std::unique_ptr<ui::devtools::protocol::CSS::CSSStyle> GetStylesForNode(