Remove RenderImage::m_needsToSetSizeForAltText

Remove another user of StyleChangeFromRenderer. This code doesn't look
needed and doesn't make sense. The test that was landed with it passes
even without the code today too.

The code came from http://trac.webkit.org/changeset/72040 and the
hasPendingStyleRecalc() check comes from
http://trac.webkit.org/changeset/72135

Checking for a pending recalc like this code did is very suspect, any
number of things can cause a recalc, or schedule one later, so checking
for a pending recalc inside the ::imageChanged callback doesn't make a
lot of sense.

Removing this code also lets us remove Document::hasPendingStyleRecalc().
In doing so I also moved methods related to the style recalc machinery
to private so people will not use them.

BUG=336552
R=ojan@chromium.org

Review URL: https://codereview.chromium.org/129873009

git-svn-id: svn://svn.chromium.org/blink/trunk@165553 bbb929c8-8fbe-4397-9dbb-9b2b20218538