Reland "Remove children from HistoryNodes that redirect during back/forward navigation"

This reverts commit 4595779d7010edec31a2224acd2a3a71a2ad206e.

BUG=334598
TEST=http/tests/navigation/back-to-redirect-with-frame.html
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/139103003

git-svn-id: svn://svn.chromium.org/blink/trunk@165535 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Allow determining if an SVG value has been specified

When checking for the "presence" of a value (if a value has been
specified - either via an attribute or via an animation), using
hasAttribute is not sufficient since if misses if the value is being
animated.

Extend the property interfaces to allow providing an answer to this query.

R=kouhei@chromium.org
TEST=svg/animations/no-attr-*.svg
BUG=330191

Review URL: https://codereview.chromium.org/141793002

git-svn-id: svn://svn.chromium.org/blink/trunk@165537 bbb929c8-8fbe-4397-9dbb-9b2b20218538