unicode-bidi: plaintext does not work properly when a line wraps

unicode-bidi: plaintext never worked properly when there is a line wrapping in a 
span with unicode-bidi: plaintext.
The problem happens because constructBidiRunsForSegment does not have
 enough logic to understand the difference between line wrapping vs line
 breaking, the current patch just adds the necessary logic(e.g when a text has a
 line wrapping it needs to determine the directionality of the paragraph from the beginning of the isolatedInline)

BUG=299879
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=158471

[leviw_travelin_and_unemployed, 2013-09-27 19:44:59]

Great! LGTM.

[commit-bot: I haz the power, 2013-09-27 19:45:09]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/igor.o@sisa.samsung.com/24998005/1

[commit-bot: I haz the power, 2013-09-27 22:35:56]

Change committed as 158471