Add MediaSessionActionDetails.isActivating (#320)

* Add MediaSessionActionDetails.isActivating
* split details dictionary

index.bs

@@ -1361,46 +1361,67 @@ should always be positive.
 
 dictionary MediaSessionActionDetails {
   required MediaSessionAction action;
-  double seekOffset;
-  double seekTime;
-  boolean fastSeek;
 };
-</pre>
 
-The {{MediaSessionActionHandler}} MUST be run with the <var>details</var>
-parameter which is represented by a dictionary inherited from
-{{MediaSessionActionDetails}}.
+dictionary MediaSessionSeekActionDetails : MediaSessionActionDetails {
+  double seekOffset;
+};
 
-The <dfn dict-member for="MediaSessionActionDetails">action</dfn> <a>dictionary
-member</a>
-is used to specify the <a>media session action</a> that the
-{{MediaSessionActionHandler}} is associated with.
+dictionary MediaSessionSeekToActionDetails : MediaSessionActionDetails {
+  required double seekTime;
+  boolean fastSeek;
+};
 
-The <dfn dict-member for="MediaSessionActionDetails">seekOffset</dfn>
-<a>dictionary member</a> MAY be provided when the <a>media session action</a>
-is {{MediaSessionAction/seekbackward}} or
-{{MediaSessionAction/seekforward}}. It is the time in seconds
-to move the playback time by. If present, it should always be positive.
-If it is not provided then the site should choose
-a sensible time (e.g. a few seconds).
+dictionary MediaSessionCaptureActionDetails : MediaSessionActionDetails {
+  boolean isActivating;
+};
 
-When the <a>media session action</a> is {{MediaSessionAction/seekto}}:
+</pre>
 
+The {{MediaSessionActionHandler}} MUST be run with the <var>details</var>
+parameter whose dictionary type is:
 <ul>
-  <li>
-    The <dfn dict-member for="MediaSessionActionDetails">seekTime</dfn>
-    <a>dictionary member</a> MUST be provided and is the time in seconds to
-    move the playback time to.
-  </li>
-
-  <li>
-    The <dfn dict-member for="MediaSessionActionDetails">fastSeek</dfn>
-    <a>dictionary member</a> MAY be provided and will be true if the
-    [=media session action|action=] is being called multiple times
-    as part of a sequence and this is not the last call in that sequence.
-  </li>
+  <li>{{MediaSessionActionDetails}} for {{MediaSessionAction/play}}.</li>
+  <li>{{MediaSessionActionDetails}} for {{MediaSessionAction/pause}}.</li>
+  <li>{{MediaSessionSeekActionDetails}} for {{MediaSessionAction/seekbackward}}.</li>
+  <li>{{MediaSessionSeekActionDetails}} for {{MediaSessionAction/seekforward}}.</li>
+  <li>{{MediaSessionActionDetails}} for {{MediaSessionAction/previoustrack}}.</li>
+  <li>{{MediaSessionActionDetails}} for {{MediaSessionAction/nexttrack}}.</li>
+  <li>{{MediaSessionActionDetails}} for {{MediaSessionAction/skipad}}.</li>
+  <li>{{MediaSessionActionDetails}} for {{MediaSessionAction/stop}}.</li>
+  <li>{{MediaSessionSeekToActionDetails}} for {{MediaSessionAction/seekto}}.</li>
+  <li>{{MediaSessionCaptureActionDetails}} for {{MediaSessionAction/togglemicrophone}}.</li>
+  <li>{{MediaSessionCaptureActionDetails}} for {{MediaSessionAction/togglecamera}}.</li>
+  <li>{{MediaSessionActionDetails}} for {{MediaSessionAction/hangup}}.</li>
+  <li>{{MediaSessionActionDetails}} for {{MediaSessionAction/previousslide}}.</li>
+  <li>{{MediaSessionActionDetails}} for {{MediaSessionAction/nextslide}}.</li>
+  <li>{{MediaSessionActionDetails}} for {{MediaSessionAction/enterpictureinpicture}}.</li>
 </ul>
 
+The <dfn dict-member for="MediaSessionActionDetails">action</dfn>
+<a>dictionary member</a> is used to specify the <a>media session action</a>
+that the {{MediaSessionActionHandler}} is associated with.
+
+The <dfn dict-member for="MediaSessionSeekActionDetails">seekOffset</dfn>
+<a>dictionary member</a> is the time in seconds to move the playback time by.
+If present, it should always be positive. If it is not provided then the site
+should choose a sensible time (e.g. a few seconds).
+
+The <dfn dict-member for="MediaSessionSeekToActionDetails">seekTime</dfn>
+<a>dictionary member</a> is the time in seconds to move the playback time to.
+
+The <dfn dict-member for="MediaSessionActionSeekToDetails">fastSeek</dfn>
+<a>dictionary member</a> will be true if the seek [=media session action|action=]
+is being called multiple times as part of a sequence and this is not the last
+call in that sequence.
+
+The <dfn dict-member for="MediaSessionActionCaptureDetails">isActivating</dfn>
+<a>dictionary member</a> will be <code>false</code> if the user agent is about
+to [=pausing all input sources|pause all input sources=] related to the capture
+[=media session action|action=] and <code>true</code> otherwise.
+This <a>dictionary member</a> MUST be present if the user agent implements a
+policy of [=pausing all input sources=].
+
 <h2 id="permissions-policy">Permissions Policy Integration</h2>
 
 This specification defines a <a>policy-controlled feature</a> identified by the