Move VisibleSelection::ChangeObserver out from VisibleSelection class

Source/core/editing/VisibleSelection.cpp

Index: Source/core/editing/VisibleSelection.cpp
diff --git a/Source/core/editing/VisibleSelection.cpp b/Source/core/editing/VisibleSelection.cpp
index be4e26ef18a8c389c49ce7d216a7914a601bd29e..4f780ba57ce27365d0f3cb6e760583a6f71a8b6f 100644
--- a/Source/core/editing/VisibleSelection.cpp
+++ b/Source/core/editing/VisibleSelection.cpp
@@ -1047,15 +1047,15 @@ Node* VisibleSelection::nonBoundaryShadowTreeRootNode() const
     return start().anchorNode() && !start().anchorNode()->isShadowRoot() ? start().anchorNode()->nonBoundaryShadowTreeRootNode() : 0;
 }
 
-VisibleSelection::ChangeObserver::ChangeObserver()
+VisibleSelectionChangeObserver::VisibleSelectionChangeObserver()
 {
 }
 
-VisibleSelection::ChangeObserver::~ChangeObserver()
+VisibleSelectionChangeObserver::~VisibleSelectionChangeObserver()
 {
 }
 
-void VisibleSelection::setChangeObserver(ChangeObserver& observer)
+void VisibleSelection::setChangeObserver(VisibleSelectionChangeObserver& observer)
 {
     ASSERT(!m_changeObserver);
     m_changeObserver = &observer;