table-caption stride over pages.

In normal block layout, pagination struts are propagated from child
blocks to parent blocks in order to indicate that an object needs to
push to the next page. Table captions were setting a pagination strut
for a push, but this strut was not being used.

Made sure RenderTable applies the caption's pagination strut when
placing the caption.

Added strut of a RenderCaption to RenderCaption's position.

BUG=329421

Review URL: https://codereview.chromium.org/80343002

git-svn-id: svn://svn.chromium.org/blink/trunk@164742 bbb929c8-8fbe-4397-9dbb-9b2b20218538