[CSS Shapes] - Bad ASSERT() in RasterShapeIntervals::firstIncludedIntervalY()

The changes for https://codereview.chromium.org/23904013 included an over-constrained ASSERT() in RasterShapeIntervals::firstIncludedIntervalY():

bool RasterShapeIntervals::firstIncludedIntervalY(int minY, const IntSize& minSize, LayoutUnit& result) const
{
    minY = std::max<int>(bounds().y(), minY);

    ASSERT(minY >= 0 && minY + minSize.height() < size());
...
}

It's only necessary for the caller to ensure that minY is effectively < size(). Legitimate calls to firstIncluedIntervalY() may specify values of minY that are greater than size() - minSize.height().

BUG=292961

Review URL: https://chromiumcodereview.appspot.com/24240004

git-svn-id: svn://svn.chromium.org/blink/trunk@158000 bbb929c8-8fbe-4397-9dbb-9b2b20218538