Bug 1342197 part 4. Move GetSelectionRange from nsTextControlFrame to the editor state. r=ehsan

At this point, all this method does is ensure editor initialization and then ask
the editor state for various information.  Let's cut out the middleman.

MozReview-Commit-ID: p491umScJO

dom/html/HTMLInputElement.h

@@ -240,6 +240,8 @@ public:
   NS_IMETHOD_(void) InitializeKeyboardEventListeners() override;
   NS_IMETHOD_(void) OnValueChanged(bool aNotify, bool aWasInteractiveUserChange) override;
   NS_IMETHOD_(bool) HasCachedSelection() override;
+  NS_IMETHOD GetSelectionRange(int32_t* aSelectionStart,
+                               int32_t* aSelectionEnd) override;
 
   void GetDisplayFileName(nsAString& aFileName) const;
 
@@ -956,8 +958,6 @@ protected:
   void SetIndeterminateInternal(bool aValue,
                                 bool aShouldInvalidate);
 
-  nsresult GetSelectionRange(int32_t* aSelectionStart, int32_t* aSelectionEnd);
-
   /**
    * Called when an attribute is about to be changed
    */