Make VTTRegion lines be a long.

Because WebIDL doesn't include an unsigned int, the VTTRegion interface
specifically calls out that negative numbers should cause an
IndexSizeError, and browser implementations are in the unsigned int,
switch over to using a regular long value.
Using a long gives us the correct range and with the definition that
specifies throwing means that negative values are not allowed.

This was discussed in the [20 June, 2019 TTWG call](https://www.w3.org/2019/06/20-tt-minutes.html#x02)

Fixes #457.

Author: gkatsev

index.bs

@@ -5926,7 +5926,7 @@ enum ScrollSetting { "" /* none */, "up" };
 interface VTTRegion {
   attribute DOMString id;
   attribute double width;
-  attribute unsigned long lines;
+  attribute long lines;
   attribute double regionAnchorX;
   attribute double regionAnchorY;
   attribute double viewportAnchorX;

index.html

@@ -1447,7 +1447,7 @@
   <div class="head">
    <p data-fill-with="logo"><a class="logo" href="https://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2016/logos/W3C" width="72"> </a> </p>
    <h1 class="p-name no-ref" id="title">WebVTT: The Web Video Text Tracks Format</h1>
-   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Draft Community Group Report, <time class="dt-updated" datetime="2018-03-30">30 March 2018</time></span></h2>
+   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Draft Community Group Report, <time class="dt-updated" datetime="2019-06-24">24 June 2019</time></span></h2>
    <div data-fill-with="spec-metadata">
     <dl>
      <dt>This version:
@@ -1472,7 +1472,7 @@ <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="cont
    </div>
    <div data-fill-with="warning"></div>
    <p class="copyright" data-fill-with="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> ©
-    2011-2018
+    2011-2019
     the Contributors to the WebVTT: The Web Video Text Tracks Format Specification, published by the <a href="http://www.w3.org/community/texttracks/">Web Media Text Tracks Community Group</a> under the <a href="https://www.w3.org/community/about/agreements/cla/">W3C Community Contributor License Agreement (CLA)</a>.
       A human-readable <a href="http://www.w3.org/community/about/agreements/cla-deed/">summary</a> is available.</p>
    <hr title="Separator for header">
@@ -5703,7 +5703,7 @@ <h3 class="heading settled algorithm" data-algorithm="The VTTRegion interface" d
 <span class="kt">interface</span> <dfn class="nv dfn-paneled idl-code" data-dfn-type="interface" data-export="" id="vttregion"><code>VTTRegion</code></dfn> {
   <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-DOMString"><span class="kt">DOMString</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="DOMString" href="#dom-vttregion-id" id="ref-for-dom-vttregion-id-1">id</a>;
   <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><span class="kt">double</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="double" href="#dom-vttregion-width" id="ref-for-dom-vttregion-width-1">width</a>;
-  <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-unsigned-long"><span class="kt">unsigned</span> <span class="kt">long</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="unsigned long" href="#dom-vttregion-lines" id="ref-for-dom-vttregion-lines-1">lines</a>;
+  <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-long"><span class="kt">long</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="long" href="#dom-vttregion-lines" id="ref-for-dom-vttregion-lines-1">lines</a>;
   <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><span class="kt">double</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="double" href="#dom-vttregion-regionanchorx" id="ref-for-dom-vttregion-regionanchorx-1">regionAnchorX</a>;
   <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><span class="kt">double</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="double" href="#dom-vttregion-regionanchory" id="ref-for-dom-vttregion-regionanchory-1">regionAnchorY</a>;
   <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><span class="kt">double</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="double" href="#dom-vttregion-viewportanchorx" id="ref-for-dom-vttregion-viewportanchorx-1">viewportAnchorX</a>;
@@ -6451,7 +6451,7 @@ <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span cla
      <li><a href="https://heycam.github.io/webidl/#indexsizeerror">IndexSizeError</a>
      <li><a href="https://heycam.github.io/webidl/#idl-boolean">boolean</a>
      <li><a href="https://heycam.github.io/webidl/#idl-double">double</a>
-     <li><a href="https://heycam.github.io/webidl/#idl-unsigned-long">unsigned long</a>
+     <li><a href="https://heycam.github.io/webidl/#idl-long">long</a>
     </ul>
   </ul>
   <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
@@ -6564,7 +6564,7 @@ <h2 class="no-num no-ref heading settled" id="idl-index"><span class="content">I
 <span class="kt">interface</span> <a class="nv" href="#vttregion"><code>VTTRegion</code></a> {
   <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-DOMString"><span class="kt">DOMString</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="DOMString" href="#dom-vttregion-id">id</a>;
   <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><span class="kt">double</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="double" href="#dom-vttregion-width">width</a>;
-  <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-unsigned-long"><span class="kt">unsigned</span> <span class="kt">long</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="unsigned long" href="#dom-vttregion-lines">lines</a>;
+  <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-long"><span class="kt">long</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="long" href="#dom-vttregion-lines">lines</a>;
   <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><span class="kt">double</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="double" href="#dom-vttregion-regionanchorx">regionAnchorX</a>;
   <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><span class="kt">double</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="double" href="#dom-vttregion-regionanchory">regionAnchorY</a>;
   <span class="kt">attribute</span> <a class="n idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><span class="kt">double</span></a> <a class="nv idl-code" data-link-type="attribute" data-type="double" href="#dom-vttregion-viewportanchorx">viewportAnchorX</a>;