[CSS Shapes] shape-outside from image doesn't load properly

Corrected a set of problems related to shape-outside image loading:

- Make RenderImage::imageChanged() call super if there's a shape-outside image, because the shape-outside imageChanged() logic is in RenderBox.

- Added the shape-outside image to appendImagesFromStyle().

- Moved the logic from RenderObject::removeShapeImageClient() from RenderObject::postDestroy() to RenderBox::willDestroy() because it's simpler that way.


BUG=360668

Review URL: https://codereview.chromium.org/226203010

git-svn-id: svn://svn.chromium.org/blink/trunk@171303 bbb929c8-8fbe-4397-9dbb-9b2b20218538