Explicit management of FrameSelection availability

third_party/WebKit/Source/core/editing/FrameSelection.h

Index: third_party/WebKit/Source/core/editing/FrameSelection.h
diff --git a/third_party/WebKit/Source/core/editing/FrameSelection.h b/third_party/WebKit/Source/core/editing/FrameSelection.h
index c42ffccd2a9c27dfead8acfa945598d4a8bc8194..3f559f5d8e23376525b5441fd06dca021b8ca0fc 100644
--- a/third_party/WebKit/Source/core/editing/FrameSelection.h
+++ b/third_party/WebKit/Source/core/editing/FrameSelection.h
@@ -93,6 +93,10 @@ public:
         return static_cast<EUserTriggered>(options & UserTriggered);
     }
 
+    bool isAvailable() const { return m_document; }
+    // You should not call |document()| when |!isAvailable()|.
+    const Document& document() const;
+    Document& document();
     LocalFrame* frame() const { return m_frame; }
     Element* rootEditableElement() const { return selection().rootEditableElement(); }
     Element* rootEditableElementOrDocumentElement() const;
@@ -121,7 +125,6 @@ public:
     bool setSelectedRange(const EphemeralRange&, TextAffinity, SelectionDirectionalMode = SelectionDirectionalMode::NonDirectional, FrameSelection::SetSelectionOptions = CloseTyping | ClearTypingStyle);
     void selectAll();
     void clear();
-    void prepareForDestruction();
 
     // Call this after doing user-triggered selections to make it easy to delete the frame you entirely selected.
     void selectFrameElementInParentIfFullySelected();
@@ -168,6 +171,8 @@ public:
     // the return value from underlying VisibleSelection's firstRange() is returned.
     Range* firstRange() const;
 
+    void documentAttached(Document*);
+    void documentDetached(const Document&);
     void nodeWillBeRemoved(Node&);
     void dataWillChange(const CharacterData& node);
     void didUpdateCharacterData(CharacterData*, unsigned offset, unsigned oldLength, unsigned newLength);
@@ -280,6 +285,7 @@ private:
     bool shouldPaintCaretForTesting() const;
     bool isPreviousCaretDirtyForTesting() const;
 
+    Member<Document> m_document;
     Member<LocalFrame> m_frame;
     const Member<PendingSelection> m_pendingSelection;
     const Member<SelectionEditor> m_selectionEditor;