Revert "[cssom-view] Kill DOMRectList. Fixes https://www.w3.org/Bugs/… (

#1499)

* Revert "[cssom-view] Kill DOMRectList. Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=26200"

This reverts commit ebc0d23.

See #1479

* grammar nit

cssom-view/Overview.bs

@@ -1080,7 +1080,7 @@ dictionary ScrollIntoViewOptions : ScrollOptions {
 };
 
 partial interface Element {
-  sequence<DOMRect> getClientRects();
+  DOMRectList getClientRects();
   [NewObject] DOMRect getBoundingClientRect();
   void scrollIntoView();
   void scrollIntoView((boolean or object) arg);
@@ -1103,9 +1103,9 @@ partial interface Element {
 
 The <dfn method for=Element>getClientRects()</dfn> method, when invoked, must return the result of the following algorithm:
 
-1. If the element on which it was invoked does not have an associated <a>layout box</a> return an empty sequence and stop this algorithm.
-1. If the element has an associated <a>SVG layout box</a> return a sequence containing a single {{DOMRect}} object that describes the bounding box of the element as defined by the SVG specification, applying the <a>transforms</a> that apply to the element and its ancestors.
-1. Return a sequence containing {{DOMRect}} objects in content order, one for each <a spec=css-break>box fragment</a>, describing its border area (including those with a height or width of zero) with the following constraints:
+1. If the element on which it was invoked does not have an associated <a>layout box</a> return an empty {{DOMRectList}} object and stop this algorithm.
+1. If the element has an associated <a>SVG layout box</a> return a {{DOMRectList}} object containing a single {{DOMRect}} object that describes the bounding box of the element as defined by the SVG specification, applying the <a>transforms</a> that apply to the element and its ancestors.
+1. Return a {{DOMRectList}} object containing {{DOMRect}} objects in content order, one for each <a spec=css-break>box fragment</a>, describing its border area (including those with a height or width of zero) with the following constraints:
 
     * Apply the <a>transforms</a> that apply to the element and its ancestors.
     * If the element on which the method was invoked has a computed value for the 'display' property of ''table'' or ''inline-table'' include both the table box and the caption box, if any, but not the anonymous container box.
@@ -1464,16 +1464,14 @@ first <a>CSS layout box</a> associated with the element, relative to the <a>init
 
 <pre class=idl>
 partial interface Range {
-  sequence&lt;DOMRect> getClientRects();
+  DOMRectList getClientRects();
   [NewObject] DOMRect getBoundingClientRect();
 };
 </pre>
 
 The <dfn method for=Range>getClientRects()</dfn> method, when invoked, must return an empty
-sequence if the range is not in the document and
-otherwise a sequence object containing
-{{DOMRect}} objects in content order that matches the
-following constraints:
+{{DOMRectList}} object if the range is not in the document and otherwise a {{DOMRectList}} object
+containing a list of {{DOMRect}} objects in content order that matches the following constraints:
 
 * For each element selected by the range, whose parent is not selected by the range, include the border areas returned by invoking {{Element/getClientRects()}} on the element.
 * For each {{Text}} node selected or partially selected by the range (including when the