Add a safe cast for RenderSliderThumb

Add a safe cast for RenderSliderThumb

Rather than a dangerous static_cast use the
DEFINE_RENDER_OBJECT_TYPE_CASTS machinery.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=183223

[rwlbuis, 2014-10-02 22:00:41]

rob.buis@samsung.com changed reviewers:
+ dsinclair@chromium.org, jchaffraix@chromium.org

[rwlbuis, 2014-10-02 22:00:54]

PTAL

[Julien - ping for review, 2014-10-03 01:08:23]

https://codereview.chromium.org/611983006/diff/1/Source/core/rendering/Render...
File Source/core/rendering/RenderSlider.cpp (right):

https://codereview.chromium.org/611983006/diff/1/Source/core/rendering/Render...
Source/core/rendering/RenderSlider.cpp:102:
static_cast<RenderSliderThumb*>(thumbBox)->updateAppearance(style());
Unguarded static_cast makes me terribly uncomfortable. By removing the virtual
isSliderThumb, this patch forces us to keep those dangerous cast around.

I would argue for keeping the function and add the appropriate cast function so
that we detect bad casts in the future.

[rwlbuis, 2014-10-03 20:15:47]

@jchaffraix PTAL, I added the safe cast and the virtual method is back...

[Julien - ping for review, 2014-10-03 22:53:57]

The CQ bit was checked by jchaffraix@chromium.org

[Julien - ping for review, 2014-10-03 22:53:58]

lgtm

[commit-bot: I haz the power, 2014-10-03 22:54:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/611983006/20001

[commit-bot: I haz the power, 2014-10-04 01:08:37]

Committed patchset #2 (id:20001) as 183223