Apply toFoo generation macro to TrackBase classes

Apply toFoo generation macro to TrackBase classes

As a step to use toFoo, this cl introduces DEFINE_TRACK_TYPE_CASTS, and use it.

BUG=309516
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178265

[gyuyoung-inactive, 2014-07-16 06:33:57]

Add haraken

[philipj_slow, 2014-07-16 07:47:40]

LGTM for Source/core/

[haraken, 2014-07-16 07:55:23]

LGTM

[gyuyoung-inactive, 2014-07-16 08:07:17]

The CQ bit was checked by gyuyoung.kim@samsung.com

[commit-bot: I haz the power, 2014-07-16 08:07:35]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/gyuyoung.kim@samsung.com/392193002/1

[commit-bot: I haz the power, 2014-07-16 09:23:08]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_blink_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_dbg/builds/1...)
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/17212)

[commit-bot: I haz the power, 2014-07-16 10:24:41]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-07-16 10:24:42]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/17231)

[gyuyoung-inactive, 2014-07-16 11:00:05]

The CQ bit was checked by gyuyoung.kim@samsung.com

[commit-bot: I haz the power, 2014-07-16 11:00:41]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/gyuyoung.kim@samsung.com/392193002/1

[commit-bot: I haz the power, 2014-07-16 11:29:49]

Change committed as 178265