DOM interface objects should have class side inheritance

To align with ES6 we should set the [[Prototype]] of the interface object to the parent interface object.

For example:

    HTMLElement.__proto__ === Element

This makes us match Firefox.

BUG=230506

Review URL: https://chromiumcodereview.appspot.com/14325010

git-svn-id: svn://svn.chromium.org/blink/trunk@155792 bbb929c8-8fbe-4397-9dbb-9b2b20218538
input[type=range]: Fix a crash by changing input type in 'input' event handler.

In SliderThumbElement::setPositionFromPoint, renderer() can be NULL
after HTMLInputElement::setValueFromRenderer, which dispatches 'input'
event. Also, make a local vairable 'input' a RefPtr just in case.

BUG=248402

Review URL: https://chromiumcodereview.appspot.com/22354003

git-svn-id: svn://svn.chromium.org/blink/trunk@155793 bbb929c8-8fbe-4397-9dbb-9b2b20218538