Add ViewObserver to View for view updates

ui/views/devtools_observer.h

Index: ui/views/devtools_observer.h
diff --git a/ui/views/devtools_observer.h b/ui/views/devtools_observer.h
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+++ b/ui/views/devtools_observer.h
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+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_VIEWS_DEVTOOLS_OBSERVER_H_
+#define UI_VIEWS_DEVTOOLS_OBSERVER_H_
+
+#include "ui/views/view.h"
+#include "ui/views/views_export.h"
+
+namespace gfx {
+class Rect;
+}
+
+namespace views {
+
+// DevTools specific observer for View changes.
+class VIEWS_EXPORT DevToolsObserver {
+ public:
+  // |view| is not necessarily the target view, but the |view|
+  // that had ViewHierarchyChanged called on it.
+  virtual void OnViewHierarchyChanged(
+      View* view,
+      const View::ViewHierarchyChangedDetails& details) {}
+
+  virtual void OnViewVisibilityChanged(View* widget, bool visible) {}
+
+  virtual void OnViewEnabledChanged(View* view, int index) {}
+
+  virtual void OnViewBoundsChanged(View* widget, const gfx::Rect& new_bounds) {}
+
+  // Invoked whenever a child is moved to another index. This is called on the
+  // parent view. |view| is the child view being reordered to the index.
+  virtual void OnChildViewReordered(View* view, int index) {}
+
+ protected:
+  virtual ~DevToolsObserver() {}
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_DEVTOOLS_OBSERVER_H_