Update WebVTT region setting parser algorithm to match the spec

https://bugs.webkit.org/show_bug.cgi?id=264736

Reviewed by Eric Carlson.

The current WebVTT parser incorrectly interprets the region id setting string `'id: foo'`
as a region with an id of `''`. However, this behavior deviates from the specification.
According to the spec, the parser should initially split the input string based on ascii spaces.
Then if the first `':'` in a setting string is either the first or last character of that string,
it should proceed to the next string. In the case of `'id: foo'`, it should be parsed as `'id:'` and `'foo'`,
both of which are considered invalid id strings.

This patch aligns the parser algorithm with the spec, which processes each setting string split by spaces.

* LayoutTests/imported/w3c/web-platform-tests/webvtt/parsing/file-parsing/tests/header-regions.html:
* LayoutTests/imported/w3c/web-platform-tests/webvtt/parsing/file-parsing/tests/regions-id-expected.txt:
* LayoutTests/imported/w3c/web-platform-tests/webvtt/parsing/file-parsing/tests/support/header-regions.vtt:
* Source/WebCore/html/track/VTTRegion.cpp:
(WebCore::VTTRegion::setRegionSettings):
(WebCore::VTTRegion::scanSettingName):

Canonical link: https://commits.webkit.org/270868@main

LayoutTests/imported/w3c/web-platform-tests/webvtt/parsing/file-parsing/tests/header-regions.html

@@ -39,7 +39,7 @@
     var testTrack = document.createElement('track');
     testTrack.onload = t.step_func_done(function() {
         var track = testTrack.track;
-        assert_equals(track.cues.length, 9);
+        assert_equals(track.cues.length, 10);
         checkCueRegions(track.cues);
     });
     testTrack.src = 'support/header-regions.vtt';

LayoutTests/imported/w3c/web-platform-tests/webvtt/parsing/file-parsing/tests/regions-id-expected.txt

@@ -1,3 +1,3 @@
 
-FAIL regions, id null is not an object (evaluating 'region3.lines')
+PASS regions, id
 

LayoutTests/imported/w3c/web-platform-tests/webvtt/parsing/file-parsing/tests/support/header-regions.vtt

@@ -24,6 +24,10 @@ REGION
 invalid_settings values but region still created
 : Invalid Header
 
+REGION
+id:region_split_by_ascii_whitespace			width:10%
+lines:5regionanchor:40%,20%    viewportanchor:30%,80% 	scroll:up
+
 00:00:00.000 --> 00:00:02.500 region:someregionattributeid
 "no region"
 
@@ -50,3 +54,6 @@ invalid_settings values but region still created
 
 00:00:07.000 --> 00:00:08.000 region:
 "no region"
+
+00:00:08.000 --> 00:00:09.000 region:region_split_by_ascii_whitespace
+{"width":10,"lines":5,"regionAnchorX":40,"regionAnchorY":20,"viewportAnchorX":30,"viewportAnchorY":80,"scroll":"up"}

Source/WebCore/html/track/VTTRegion.cpp

@@ -143,41 +143,42 @@ void VTTRegion::updateParametersFromRegion(const VTTRegion& other)
 
 void VTTRegion::setRegionSettings(const String& inputString)
 {
+    // https://w3c.github.io/webvtt/#region-settings-parsing
+    // 6.2. WebVTT region settings parsing
     m_settings = inputString;
     VTTScanner input(inputString);
 
     while (!input.isAtEnd()) {
-        input.skipWhile<isTabOrSpace>();
-        if (input.isAtEnd())
-            break;
+        // Step 1 - Split input on spaces.
+        input.skipWhile<isASCIIWhitespace<UChar>>();
+        VTTScanner::Run valueRun = input.collectUntil<isASCIIWhitespace<UChar>>();
+        VTTScanner setting(input.extractString(valueRun));
 
-        // Scan the name part.
-        RegionSetting name = scanSettingName(input);
+        // Step 2.2 - Let name be the leading substring of setting up to and excluding the first U+003A COLON character (:) in that string.
+        RegionSetting name = scanSettingName(setting);
 
-        // Verify that we're looking at a ':'.
-        if (name == None || !input.scan(':')) {
-            input.skipUntil<isASCIIWhitespace<UChar>>();
+        // Step 2.1 - If the first ':' in setting is the last character of setting, then jump to the next setting.
+        if (name == None || setting.isAtEnd())
             continue;
-        }
 
-        // Scan the value part.
-        parseSettingValue(name, input);
+        // Steps 2.3-2.4 - Scan the value part.
+        parseSettingValue(name, setting);
     }
 }
 
 VTTRegion::RegionSetting VTTRegion::scanSettingName(VTTScanner& input)
 {
-    if (input.scan("id"))
+    if (input.scan("id:"))
         return Id;
-    if (input.scan("lines"))
+    if (input.scan("lines:"))
         return Lines;
-    if (input.scan("width"))
+    if (input.scan("width:"))
         return Width;
-    if (input.scan("viewportanchor"))
+    if (input.scan("viewportanchor:"))
         return ViewportAnchor;
-    if (input.scan("regionanchor"))
+    if (input.scan("regionanchor:"))
         return RegionAnchor;
-    if (input.scan("scroll"))
+    if (input.scan("scroll:"))
         return Scroll;
 
     return None;