Don't find(':') twice in WebVTTParser::collectMetadataHeader

Source/core/html/track/vtt/VTTParser.cpp

Index: Source/core/html/track/vtt/VTTParser.cpp
diff --git a/Source/core/html/track/vtt/VTTParser.cpp b/Source/core/html/track/vtt/VTTParser.cpp
index cddec3461f1916dfc75893afe5b7998e3809b204..fffc502f137bdc963b7694afdf2ff873b68919cf 100644
--- a/Source/core/html/track/vtt/VTTParser.cpp
+++ b/Source/core/html/track/vtt/VTTParser.cpp
@@ -244,13 +244,17 @@ void WebVTTParser::collectMetadataHeader(const String& line)
     // WebVTT header parsing (WebVTT parser algorithm step 12)
     DEFINE_STATIC_LOCAL(const AtomicString, regionHeaderName, ("Region", AtomicString::ConstructFromLiteral));
 
+    // The only currently supported header is the "Region" header.
+    if (!RuntimeEnabledFeatures::webVTTRegionsEnabled())
+        return;
+
     // Step 12.4 If line contains the character ":" (A U+003A COLON), then set metadata's
     // name to the substring of line before the first ":" character and
     // metadata's value to the substring after this character.
-    if (!RuntimeEnabledFeatures::webVTTRegionsEnabled() || !line.contains(":"))
+    unsigned colonPosition = line.find(':');
+    if (colonPosition == kNotFound)
         return;
 
-    unsigned colonPosition = line.find(":");
     String headerName = line.substring(0, colonPosition);
 
     // Steps 12.5 If metadata's name equals "Region":