WebVTT: Support fractional percentage values for position/line/size

LayoutTests/media/track/opera/track/webvtt/parsing/support/settings-position.vtt

 WEBVTT
 
 00:00:00.000 --> 00:00:01.000 position:-1%
 {}
 
+00:00:00.000 --> 00:00:01.000 position:-1.5%
+{}
+
 00:00:00.000 --> 00:00:01.000 position:1
 {}
 
+00:00:00.000 --> 00:00:01.000 position:1.5

[philipj_slow, 2015/01/22 12:55:44]

Maybe test with 1.0 to check that it's not just a matter of the result having a
zero fractional part.

[fs, 2015/01/22 13:17:06]

Done.

+{}
+
+00:00:00.000 --> 00:00:01.000 position:-50.25
+{}
+
 00:00:00.000 --> 00:00:01.000 position:1x
 {}
 
 00:00:00.000 --> 00:00:01.000 position:1%x
 {}
 
 00:00:00.000 --> 00:00:01.000 position:
 {}
 
 00:00:00.000 --> 00:00:01.000 position: 1%
 {}
 
 00:00:00.000 --> 00:00:01.000 position:1%
 {"position":1}
 
 00:00:00.000 --> 00:00:01.000 position:100%
 {"position":100}
 
 00:00:00.000 --> 00:00:01.000 position:101%
 {}
 
 00:00:00.000 --> 00:00:01.000 position:1% position:x
 {"position":1}
 
 00:00:00.000 --> 00:00:01.000 position:1.5%
-{}
+{"position":1.5}
+
+00:00:00.000 --> 00:00:01.000 position:10.25%
+{"position":10.25}
 
 00:00:00.000 --> 00:00:01.000 position:65536%
 {}
 
 00:00:00.000 --> 00:00:01.000 position:4294967296%
-{}
+{}
+
+00:00:00.000 --> 00:00:01.000 position:.5%
+{"position":0.5}
+
+00:00:00.000 --> 00:00:01.000 position:5.%
+{"position":5}