Add a use counter for VTTCue right-to-left rendering

Add a use counter for VTTCue right-to-left rendering

The WebVTT position model has been changed:
https://www.w3.org/Bugs/Public/show_bug.cgi?id=20037

In order to ship this (or any alternative) we need to know that it
doesn't break too much, and right-to-left text used to flip the
interpretation of the position setting, but doesn't any longer.

BUG=none

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=173841

[fs, 2014-05-11 20:23:18]

LGTM

[philipj_slow, 2014-05-11 20:28:45]

The CQ bit was checked by philipj@opera.com

[commit-bot: I haz the power, 2014-05-11 20:28:49]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/philipj@opera.com/276193002/1

[commit-bot: I haz the power, 2014-05-11 21:11:02]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  linux_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/6927)

[commit-bot: I haz the power, 2014-05-11 21:49:11]

Change committed as 173841

[commit-bot: I haz the power, 2014-05-11 21:49:26]

Failed to apply patch for Source/core/frame/UseCounter.h:
While running patch -p1 --forward --force --no-backup-if-mismatch;
  patching file Source/core/frame/UseCounter.h
  Hunk #1 FAILED at 420.
  1 out of 1 hunk FAILED -- saving rejects to file
Source/core/frame/UseCounter.h.rej

Patch:       Source/core/frame/UseCounter.h
Index: Source/core/frame/UseCounter.h
diff --git a/Source/core/frame/UseCounter.h b/Source/core/frame/UseCounter.h
index
bb030c5917caab40408b7802b8bc36698920fc44..c1d8d3ac32d5f68732382a1de7389d9bd77af365
100644
--- a/Source/core/frame/UseCounter.h
+++ b/Source/core/frame/UseCounter.h
@@ -420,6 +420,7 @@ public:
         VTTCueRenderSizeNot100 = 415,
         VTTCueRenderAlignNotMiddle = 416,
         ElementRequestPointerLock = 417,
+        VTTCueRenderRtl = 418,
         // Add new features immediately above this line. Don't change assigned
         // numbers of any item, and don't reuse removed slots.
         // Also, run update_use_counter_feature_enum.py in
chromium/src/tools/metrics/histograms/