Added method of getting top genID from SkClipStack

This CL actually has two methods of getting the top genID from SkClipStack. One is through SkClipStack::getTopmostGenID(). The other is using the fGenID field of the Clip object returned by the iterator. The method that actually implements that technique lives in an as yet undelivered file and is:

int32_t get_topmost_genID(const SkClipStack& clip) {
    SkClipStack::Iter iter(clip, SkClipStack::Iter::kTop_IterStart);

    const SkClipStack::Iter::Clip* temp = iter.prev();
    if (NULL == temp) {
        return SkClipStack::kInvalidGenID;
    }

    return temp->fGenID;
}

[bsalomon, 2012-08-09 18:00:19]

On 2012/08/09 17:28:27, robertphillips wrote:

LGTM

[robertphillips, 2012-08-09 18:11:10]

committed as r5034