Move text track active list management to CueTimeline

Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/AnimationEffect.idl',
             'animation/AnimationNode.idl',
@@ skipping 3022 matching lines @@
             'html/shadow/SpinButtonElement.cpp',
             'html/shadow/SpinButtonElement.h',
             'html/shadow/TextControlInnerElements.cpp',
             'html/shadow/TextControlInnerElements.h',
             'html/track/AudioTrack.cpp',
             'html/track/AudioTrack.h',
             'html/track/AudioTrackList.cpp',
             'html/track/AudioTrackList.h',
             'html/track/AutomaticTrackSelection.cpp',
             'html/track/AutomaticTrackSelection.h',
+            'html/track/CueTimeline.cpp',
+            'html/track/CueTimeline.h',
             'html/track/InbandTextTrack.cpp',
             'html/track/InbandTextTrack.h',
             'html/track/LoadableTextTrack.cpp',
             'html/track/LoadableTextTrack.h',
             'html/track/TextTrack.cpp',
             'html/track/TextTrack.h',
             'html/track/TextTrackCue.cpp',
             'html/track/TextTrackCue.h',
             'html/track/TextTrackCueList.cpp',
             'html/track/TextTrackCueList.h',
@@ skipping 750 matching lines @@
             'rendering/RenderingTestHelper.h',
             'streams/ExclusiveStreamReaderTest.cpp',
             'streams/ReadableStreamTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }