Improve comparison of intervals in SVGSMILElement::resolveFirstInterval

For open-ended intervals such as [3) - i.e. begin=3s and end/duration/etc
unspecified - every call to resolveFirstInterval() would think that a new
interval had been created, and notify/require a reschedule of the
animations.
Add a new type SMILInterval and a suitable operator for that, and then
use it to compare the raw values (i.e. if both endpoints are exacly the same.)

BUG=377329

Review URL: https://codereview.chromium.org/298043005

git-svn-id: svn://svn.chromium.org/blink/trunk@175122 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Scrollbar width is not applied when element hidden

Webkit has css properties through which custom scroll bars can be added.
In case the element's visibility property is hidden and custom scrollbar 
properties are applied the scrollbar width is not considered when querying
the element.clientWidth. In case of non-custom scrollbars whether the
element's visibility property is hidden or not correct scrollbar width is
considered.

When a custom scrollbar is created there is a check whether the renderer to
which scrollbar is added is visible or not. This check is not required since
for non-custom scrollbars the same check is not present. Also whether the
element's visibility property is hidden or not a placeholder is set for the
element.

Both behavior i.e custom and non-custom scrollbars should be same.

I already landed this patch on Webkit. Just modified the layout test file.
http://trac.webkit.org/changeset/155323

R=esprehn@chromium.org,eseidel@chromium.org
BUG=343521

Review URL: https://codereview.chromium.org/163383002

git-svn-id: svn://svn.chromium.org/blink/trunk@175123 bbb929c8-8fbe-4397-9dbb-9b2b20218538