Clarify the size of a document view (a.k.a layout size) that causes FrameView to emit the resize event.

The spec DOM Level 2 Events states that the resize event occurs when a document
view is resized. Refer to

After WebKit r141053, ScrollView::unscaledVisibleContentSize stands for a layout size.
When turning on fixed layout, fixed layout size stands for a layout size. There
is already ScrollView::layoutSize() method matching above explanation.

However, this issue introduced viewportSize() to include scrollbars. We don't
want that showing/hiding scrollbars is considered a layout size change. Refer to

TEST=fast/events/resize-events.html, fast/events/resize-events-count.html, fast/events/resize-events-fixed-layout.html

Review URL:

git-svn-id: svn:// bbb929c8-8fbe-4397-9dbb-9b2b20218538
7 files changed