Remove SVGElement::childShouldCreateRenderer

All implementation now return true, and the RenderObject::isChildAllowed
mechanism is used instead.

BUG=337607

Review URL: https://codereview.chromium.org/157663002

git-svn-id: svn://svn.chromium.org/blink/trunk@166733 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove forceUpdate bool that is never used.

Review URL: https://codereview.chromium.org/157583004

git-svn-id: svn://svn.chromium.org/blink/trunk@166734 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Use IDL enum to ignore invalid SourceBuffer mode attribute setting

Adheres to current MediaSource's SourceBuffer mode attribute spec that
uses a WebIDL enum for AppendMode. In this case, scripts' attempts to
set invalid mode attribute values outside the range of the enum now
result in the attempts being ignored, as WebIDL spec requires.
Updates mediasource-sourcebuffer-mode layout test accordingly.

R=acolwell@chromium.org
BUG=249422
TEST=Updated layout test passes on local linux.

Review URL: https://codereview.chromium.org/156853005

git-svn-id: svn://svn.chromium.org/blink/trunk@166735 bbb929c8-8fbe-4397-9dbb-9b2b20218538