[web-animations-1] Fixed play animation procedure for scroll animations (w3c#2075) (w3c#5059)

* Fixed play animation procedure for scroll animations.

* Refactored play and pause procedures.

Author: ogerchikov

web-animations-1/Overview.bs

@@ -1140,7 +1140,7 @@ as CSS Animations [[CSS-ANIMATIONS-1]].
     <var>animation</var> has a <a>pending pause task</a>, and false otherwise.
 1.  Let <var>has pending ready promise</var> be a boolean flag that is
     initially false.
-1.  Let <var>performed seek</var> be a boolean flag that is initially false.
+1.  Let <var>seek time</var> be a <a>time value</a> that is initially <a>unresolved</a>.
 1.  Let <var>has finite timeline</var> be true if |animation| has an associated
     <a>timeline</a> that is not [=monotonically increasing=].
 1.  Perform the steps corresponding to the <em>first</em> matching
@@ -1156,18 +1156,7 @@ as CSS Animations [[CSS-ANIMATIONS-1]].
         *   <a>current time</a> &lt; zero, or
         *   <a>current time</a> &ge; <a>associated effect end</a>,
 
-    ::  1.  Set <var>performed seek</var> to true.
-        1.  Update either <var>animation</var>’s <a>start time</a> or
-            <a>hold time</a> as follows:
-
-            <div class="switch">
-
-            :   If |has finite timeline| is true,
-            ::  Set <var>animation</var>'s <a>start time</a> to zero.
-            :   Otherwise,
-            ::  Set <var>animation</var>'s <a>hold time</a> to zero.
-
-            </div>
+    ::  Set <var>seek time</var> to zero.
 
     :   If |animation|'s [=effective playback rate=] &lt; 0,
         the <var>auto-rewind</var> flag is true and <em>either</em>
@@ -1183,40 +1172,32 @@ as CSS Animations [[CSS-ANIMATIONS-1]].
         ::  <a>throw</a> an "{{InvalidStateError}}" {{DOMException}} and
             abort these steps.
         :   Otherwise,
-        ::  1.  Set <var>performed seek</var> to true.
-            1.  Update either <var>animation</var>’s <a>start time</a> or
-                <a>hold time</a> as follows:
-
-                <div class="switch">
-
-                :   If |has finite timeline| is true,
-                ::  Set <var>animation</var>'s <a>start time</a> to <a>associated
-                    effect end</a>.
-                :   Otherwise,
-                ::  Set <var>animation</var>'s <a>hold time</a> to <a>associated
-                    effect end</a>.
-
-                </div>
+        ::  Set <var>seek time</var> to |animation|'s <a>associated effect end</a>.
 
         </div>
 
     :   If |animation|'s [=effective playback rate=] = 0 and |animation|'s
         [=current time=] is [=unresolved=],
 
-        ::  1.  Set <var>performed seek</var> to true.
-            1.  Update either <var>animation</var>’s <a>start time</a> or
-                <a>hold time</a> as follows:
+        ::  Set <var>seek time</var> to zero.
+
+    </div>
 
-                <div class="switch">
+1.  If |seek time| is <a lt=unresolved>resolved</a>,
+     
+        <div class="switch">
 
-                :   If |has finite timeline| is true,
-                ::  Set <var>animation</var>'s <a>start time</a> to zero.
-                :   Otherwise,
-                ::  Set <var>animation</var>'s <a>hold time</a> to zero.
+        :   If |has finite timeline| is true,
+        ::  1.  Set <var>animation</var>'s <a>start time</a> to <var>seek time</var>.
+            1.  Let |animation|'s [=hold time=] be <a>unresolved</a>.
+            1.  [=Apply any pending playback rate=] on |animation|.
+        :   Otherwise,
+        ::  Set <var>animation</var>'s <a>hold time</a> to <var>seek time</var>.
 
-                </div>
+        </div>
 
-    </div>
+1.  If <var>animation</var>'s <a>hold time</a> is <a lt=unresolved>resolved</a>,
+    let its [=start time=] be <a>unresolved</a>.
 
 1.  If <var>animation</var> has a <a>pending play task</a> or a
     <a>pending pause task</a>,
@@ -1227,15 +1208,12 @@ as CSS Animations [[CSS-ANIMATIONS-1]].
 1.  If the following four conditions are <em>all</em> satisfied:
 
     * |animation|'s [=hold time=] is [=unresolved=], and
-    * |performed seek| is false, and
+    * |seek time| is [=unresolved=], and
     * |aborted pause| is false, and
     * |animation| does <em>not</em> have a [=pending playback rate=],
 
     abort this procedure.
 
-1.  If <var>animation</var>'s <a>hold time</a> is <a lt=unresolved>resolved</a>,
-    let its [=start time=] be <a>unresolved</a>.
-
 1.  If <var>has pending ready promise</var> is false,
     let <var>animation</var>'s <a>current ready promise</a> be
     <a>a new promise</a> in the <a>relevant Realm</a> of <var>animation</var>.
@@ -1360,6 +1338,7 @@ follows:
 1.  If <var>animation</var> has a <a>pending pause task</a>, abort these steps.
 1.  If the <a>play state</a> of <var>animation</var> is <a
     lt="paused play state">paused</a>, abort these steps.
+1.  Let <var>seek time</var> be a <a>time value</a> that is initially <a>unresolved</a>.
 1.  Let <var>has finite timeline</var> be true if |animation| has an associated
     <a>timeline</a> that is not [=monotonically increasing=].
 1.  If the <var>animation</var>'s <a>current time</a> is <a>unresolved</a>,
@@ -1368,18 +1347,7 @@ follows:
     <div class="switch">
 
     :   If <var>animation</var>'s [=playback rate=] is &ge; 0,
-    ::  Update either <var>animation</var>’s <a>start time</a> or
-        <a>hold time</a> as follows:
-
-        <div class="switch">
-
-        :   If |has finite timeline| is true,
-        ::  Set <var>animation</var>'s <a>start time</a> to zero.
-        :   Otherwise,
-        ::  Set <var>animation</var>'s <a>hold time</a> to zero.
-
-        </div>
-
+    ::  Set <var>seek time</var> to zero.
     :   Otherwise,
     ::
         <div class="switch">
@@ -1389,23 +1357,23 @@ follows:
         ::  <a>throw</a> an "{{InvalidStateError}}" {{DOMException}}
             and abort these steps.
         :   Otherwise,
-        ::  Update either <var>animation</var>’s <a>start time</a> or
-            <a>hold time</a> as follows:
+        ::  Set <var>seek time</var> to <var>animation</var>'s <a>associated effect
+            end</a>.
 
-            <div class="switch">
+        </div>
 
-            :   If |has finite timeline| is true,
-            ::  let <var>animation</var>'s <a>start time</a> be
-                <a>associated effect end</a>.
-            :   Otherwise,
-            ::  let <var>animation</var>'s <a>hold time</a> be
-                <a>associated effect end</a>.
+    </div>
 
-            </div>
+1.  If |seek time| is <a lt=unresolved>resolved</a>,
 
-        </div>
+        <div class="switch">
 
-    </div>
+        :   If |has finite timeline| is true,
+        ::  Set <var>animation</var>'s <a>start time</a> to <var>seek time</var>.
+        :   Otherwise,
+        ::  Set <var>animation</var>'s <a>hold time</a> to <var>seek time</var>.
+
+        </div>
 
 1.  Let <var>has pending ready promise</var> be a boolean flag that is
     initially false.