[cssom-view-1] Add emulation for "Web-exposed screen information" with WebDriver BiDi.

Author: lutien

cssom-view-1/Overview.bs

@@ -55,6 +55,7 @@ spec:css-borders-4; type:property; text:border-top-width
 spec:css-borders-4; type:property; text:border-left-width
 spec:cssom-view-1; type:dictionary; text:MouseEventInit
 spec:cssom-view-1; type:dfn; for:MediaQueryList; text:media
+spec:webdriver-bidi; type:dfn; text:WebDriver BiDi emulated screen area
 </pre>
 
 <style>
@@ -413,16 +414,24 @@ protect the user's privacy. In order to do so in a consistent manner across APIs
 defines the following terms, each having a width and a height, the origin being the top left
 corner, and the x- and y-coordinates increase rightwards and downwards, respectively.
 
-The <dfn export>Web-exposed screen area</dfn> is one of the following:
+The <dfn export>Web-exposed screen area</dfn> must return the result of the following algorithm:
 
-* The area of the output device, in <a lt=px value>CSS pixels</a>.
-* The area of the <a>viewport</a>, in <a lt=px value>CSS pixels</a>.
+1. Let <var>target</var> be [=this=]'s [=relevant global object=]'s [=Window/browsing context=].
+1. Let |emulated screen area| be the <a>WebDriver BiDi emulated screen area</a> for <var>target</var>.
+1. If |emulated screen area| is not null, return |emulated screen area|.
+1. Otherwise, return one of the following:
+    * The area of the output device, in <a lt=px value>CSS pixels</a>.
+    * The area of the <a>viewport</a>, in <a lt=px value>CSS pixels</a>.
 
-The <dfn export>Web-exposed available screen area</dfn> is one of the following:
+The <dfn export>Web-exposed available screen area</dfn> must return the result of the following algorithm:
 
-* The available area of the rendering surface of the output device, in <a lt=px value>CSS pixels</a>.
-* The area of the output device, in <a lt=px value>CSS pixels</a>.
-* The area of the <a>viewport</a>, in <a lt=px value>CSS pixels</a>.
+1. Let <var>target</var> be [=this=]'s [=relevant global object=]'s [=Window/browsing context=].
+1. Let |emulated screen area| be the <a>WebDriver BiDi emulated screen area</a> for <var>target</var>.
+1. If |emulated screen area| is not null, return |emulated screen area|.
+1. Otherwise, return one of the following:
+    * The available area of the rendering surface of the output device, in <a lt=px value>CSS pixels</a>.
+    * The area of the output device, in <a lt=px value>CSS pixels</a>.
+    * The area of the <a>viewport</a>, in <a lt=px value>CSS pixels</a>.
 
 
 <h2 id=common-infrastructure>Common Infrastructure</h2>