Implement VTTCue.region and sync the VTTRegion interface

third_party/WebKit/LayoutTests/media/track/captions-webvtt/header-regions.vtt

 WEBVTT FILE
 Region: id=region_without_settings
 Region: id=region_with_all_settings width=32% height=5 regionanchor=41%,20% viewportanchor=31%,84% scroll=up
-Region: id=region_floating_point_anchor regionanchor=41.133%,20.42% viewportanchor=32.33%,32.44%
+Region: id=region_floating_point_anchor regionanchor=41.125%,20.25% viewportanchor=32.75%,32.5%
 Region: id=not_unique_id width=42%
 Region: id=not_unique_id width=67%
 Region: invalid_settings values but region still created
 : Invalid Header
 
-1
 00:00:00.000 --> 00:00:02.500 region:someregionattributeid
-We are in New York City
+"no region"
 
-2
 00:00:00.000 --> 00:00:02.500 line:5 region:ignored_attribute_value
-Line is specified, Region should be ignored.
+"no region"
 
-3
 00:00:00.000 --> 00:00:02.500 size:10% region:ignored_attribute_value
-Size is specified, Region should be ignored.
+"no region"
 
-4
 00:00:00.000 --> 00:00:02.500 vertical:lr region:ignored_attribute_value
-Vertical is specified, Region should be ignored.
+"no region"
+
+00:00:03.000 --> 00:00:04.000 region:region_without_settings
+{}
+
+00:00:04.000 --> 00:00:05.000 region:region_with_all_settings
+{"width":32,"lines":5,"regionAnchorX":41,"regionAnchorY":20,"viewportAnchorX":31,"viewportAnchorY":84,"scroll":"up"}
+
+00:00:05.000 --> 00:00:06.000 region:region_floating_point_anchor
+{"regionAnchorX":41.125,"regionAnchorY":20.25,"viewportAnchorX":32.75,"viewportAnchorY":32.5}
+
+00:00:06.000 --> 00:00:07.000 region:not_unique_id
+{"width":67}
+
+00:00:07.000 --> 00:00:08.000 region:
+"no region"