Iron out some kinks in SVG IDL files

This drops a few "[Default=Undefined] optional" from method arguments to
match the expected arity checking behavior.
Matches Gecko and the spec where applicable.

For SVGAnimationElement.{begin,end}ElementAt, block all non-finite values
as per the WebIDL 'float' type.

BUG=311246

Review URL: https://codereview.chromium.org/231143002

git-svn-id: svn://svn.chromium.org/blink/trunk@171485 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Network Panel: show "Disable Cache" checkbox.

It makes easier tracking/switching this option.

Screenshot: http://picpaste.com/disableNetwork.png

BUG=333579

Review URL: https://codereview.chromium.org/216233004

git-svn-id: svn://svn.chromium.org/blink/trunk@171486 bbb929c8-8fbe-4397-9dbb-9b2b20218538