Replace manual pointer arithmetic with WTF:Vector in Gradient::shader()

Replace manual pointer arithmetic with WTF::Vector in Gradient::shader()

It's more idiomatic to use a vector for a dynamically-sized array; it also 
provides a convenient opportunity to use inline capacity in the common case
where a gradient has a small number of stops.

BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169686

[jbroman, 2014-03-20 18:40:06]

While looking at WebCore::Gradient, I noticed a FIXME complaining about pointer
arithmetic. I looked at what it would look like to use WTF::Vector instead.

I'm not sure whether this is worth landing (the existing logic is a little
unusual in Blink, but not hard to understand), so feel free to tell me if you
think I should just drop this CL, and I will. :)

[Stephen Chennney, 2014-03-20 19:03:55]

LBTM. I think it's worth doing to make life a bit cleaner. Given the small size
of the typical stops vector there's no harm in Vector.

[Stephen Chennney, 2014-03-20 19:04:22]

On 2014/03/20 19:03:55, Stephen Chenney wrote:
> LBTM. I think it's worth doing to make life a bit cleaner. Given the small
size
> of the typical stops vector there's no harm in Vector.

That's LGTM.

[jbroman, 2014-03-20 19:11:20]

The CQ bit was checked by jbroman@chromium.org

[commit-bot: I haz the power, 2014-03-20 19:11:21]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jbroman@chromium.org/201523002/20001

[commit-bot: I haz the power, 2014-03-20 19:13:56]

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

[commit-bot: I haz the power, 2014-03-20 19:13:56]

Try jobs failed on following builders:
  tryserver.blink on win_blink_compile_dbg

[jbroman, 2014-03-20 19:27:15]

The CQ bit was checked by jbroman@chromium.org

[commit-bot: I haz the power, 2014-03-20 19:27:21]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jbroman@chromium.org/201523002/20001

[commit-bot: I haz the power, 2014-03-20 20:00:03]

Change committed as 169686