Do not change input/textarea text selection for the same value

Fixes whatwg#2412.

source

@@ -48644,6 +48644,9 @@ You cannot submit this form when the field is incorrect.</samp></pre>
     <p>On setting:</p>
 
     <ol>
+     <li><p>Let <var>oldValue</var> be the element's <span
+     data-x="concept-fe-value">value</span>.</p></li>
+
      <li><p>Set the element's <span data-x="concept-fe-value">value</span> to the new
      value.</p></li>
 
@@ -48653,9 +48656,10 @@ You cannot submit this form when the field is incorrect.</samp></pre>
      <li><p>Invoke the <span>value sanitization algorithm</span>, if the element's <code
      data-x="attr-input-type">type</code> attribute's current state defines one.</p></li>
 
-     <li><p>If the element has a text entry cursor position, move the text entry cursor position to
-     the end of the text control, unselecting any selected text and <span data-x="set the selection
-     direction">resetting the selection direction</span> to "<code data-x="">none</code>".</p></li>
+     <li><p>If the new value is different from <var>oldValue</var> and the element has a text entry
+     cursor position, move the text entry cursor position to the end of the text control,
+     unselecting any selected text and <span data-x="set the selection direction">resetting the
+     selection direction</span> to "<code data-x="">none</code>".</p></li>
     </ol>
    </dd>
 
@@ -50625,15 +50629,19 @@ interface <dfn>HTMLTextAreaElement</dfn> : <span>HTMLElement</span> {
   perform the following steps:</p>
 
   <ol>
+   <li><p>Let <var>oldAPIValue</var> be this element's <span
+   data-x="concept-fe-api-value">API value</span>.</p></li>
+
    <li><p>Set this element's <span data-x="concept-textarea-raw-value">raw value</span> to the new
    value.</p></li>
 
    <li><p>Set this element's <span data-x="concept-fe-dirty">dirty value flag</span> to
    true.</p></li>
 
-   <li><p>Move the text entry cursor position to the end of the text control, unselecting any
-   selected text and <span data-x="set the selection direction">resetting the selection
-   direction</span> to "<code data-x="">none</code>".</p></li>
+   <li><p>If the new <span data-x="concept-fe-api-value">API value</span> is different from
+   <var>oldAPIValue</var>, then move the text entry cursor position to the end of the text control,
+   unselecting any selected text and <span data-x="set the selection direction">resetting the
+   selection direction</span> to "<code data-x="">none</code>".</p></li>
   </ol>
 
   <p>The <dfn><code data-x="dom-textarea-textLength">textLength</code></dfn> IDL attribute must