Convert LayoutState/LayoutStateMaintainer/LayoutStateDisabler to references

Convert LayoutState/LayoutStateMaintainer/LayoutStateDisabler to references when
possible.  This is very much in the same spirit as r159391 in WebKit, but goes a
little further in converting to references where possible.  I've also taken the
opportunity to convert LayoutStateDisabler to take a RenderObject instead of the
view.  Also, FrameView gets a new RAII class to simplify code in performLayout.

BUG=None

Review URL: https://codereview.chromium.org/164553004

git-svn-id: svn://svn.chromium.org/blink/trunk@167724 bbb929c8-8fbe-4397-9dbb-9b2b20218538
plain/text is not a real MIME type.

Change to 'text/plain'.

BUG=none

Review URL: https://codereview.chromium.org/176873007

git-svn-id: svn://svn.chromium.org/blink/trunk@167725 bbb929c8-8fbe-4397-9dbb-9b2b20218538