Use and add layout tests for BCP 47 language tag syntax validation.

Source/modules/mediasource/TrackDefault.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "modules/mediasource/TrackDefault.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/html/track/AudioTrack.h"
 #include "core/html/track/TextTrack.h"
 #include "core/html/track/VideoTrack.h"
+#include "public/platform/Platform.h"
 
 namespace blink {
 
 static const AtomicString& audioKeyword()
 {
     DEFINE_STATIC_LOCAL(const AtomicString, audio, ("audio", AtomicString::ConstructFromLiteral));
     return audio;
 }
 
 static const AtomicString& videoKeyword()
@@ skipping 10 matching lines @@
 
 TrackDefault* TrackDefault::create(const AtomicString& type, const String& language, const String& label, const Vector<String>& kinds, const String& byteStreamTrackID, ExceptionState& exceptionState)
 {
     // Per 11 Nov 2014 Editor's Draft
     // https://dvcs.w3.org/hg/html-media/raw-file/tip/media-source/media-source.html#idl-def-TrackDefault
     // with expectation that
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=27352 will be fixed soon:
     // When this method is invoked, the user agent must run the following steps:
     // 1. if |language| is not an empty string and |language| is not a BCP 47
     //    language tag, then throw an INVALID_ACCESS_ERR and abort these steps.
-    // FIXME: Implement BCP 47 language tag validation.
+    if (!Platform::current()->isValidLocaleSyntax(language)) {
+        exceptionState.throwDOMException(InvalidAccessError, "Invalid BCP 47 language tag");
+        return nullptr;
+    }
 
     if (type == audioKeyword()) {
         // 2.1. If |type| equals "audio":
         //      If any string in |kinds| contains a value that is not listed as
         //      applying to audio in the kind categories table, then throw a
         //      TypeError and abort these steps.
         for (const String& kind : kinds) {
             if (!AudioTrack::isValidKindKeyword(kind)) {
                 exceptionState.throwTypeError("Invalid audio track default kind '" + kind + "'");
                 return nullptr;
@@ skipping 43 matching lines @@
 TrackDefault::TrackDefault(const AtomicString& type, const String& language, const String& label, const Vector<String>& kinds, const String& byteStreamTrackID)
     : m_type(type)
     , m_byteStreamTrackID(byteStreamTrackID)
     , m_language(language)
     , m_label(label)
     , m_kinds(kinds)
 {
 }
 
 } // namespace blink