Add toSVGPolylineElement(), and use it

As a step to clean-up static_cast<SVGXXX>, toSVGPolylineElement() is added in order to clean-up
static_cast<SVGPolylineElement*>.

BUG=N/A

Review URL: https://chromiumcodereview.appspot.com/23583011

git-svn-id: svn://svn.chromium.org/blink/trunk@156947 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Refactoring: Remove Event::create(const AtomicString&, bool, bool).

Add Event::createCancelableBubble(), and replace all of existing call
sites of Event::create with bool arguments with new factory functions.

BUG=none
TEST=none; no behavior changes.

Review URL: https://chromiumcodereview.appspot.com/23490016

git-svn-id: svn://svn.chromium.org/blink/trunk@156949 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove a remaining Event::create(const AtomicString&, bool, bool) call.

BUG=none
TBR=morrita@chromium.org

Review URL: https://codereview.chromium.org/23808002

git-svn-id: svn://svn.chromium.org/blink/trunk@156950 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add ImageObserverDisabler for disabling the image observer in SVG images

This change adds a new class for disabling the image observer in
SVGImage.cpp which is used for hiding the fact that we re-use a single
SVG document in multiple instances. This is a cleanup in prep for a
larger patch in crbug.com/279445.

Also in this patch is a cleanup making SVGImage::frameView() private
to prevent well meaning coders from accidentally leaking the SVG
document's FrameView.

R=esprehn
BUG=279445

Review URL: https://chromiumcodereview.appspot.com/23490014

git-svn-id: svn://svn.chromium.org/blink/trunk@156951 bbb929c8-8fbe-4397-9dbb-9b2b20218538