Move m_valueMatchesRenderer flag to HTMLInputElement and HTMLTextAreaElement.

m_valueMatchesRenderer was defined in HTMLFormControlElement, but only <input>
and <textarea> use it. So we move the flag to their implementation classes.

We have the common base class of HTMLInputElement and HTMLTextAreaElement,
HTMLTextFormControlElement. However this CL doesn't move the flag to
HTMLTextFormControlElement because the purposes of the flag are different in
HTMLInputElement and HTMLTextAreaElement.

Note:
We need to make setInnerText virtual, and override it in HTMLInputElement and
HTMLTextAreaElement because m_valueMatchesRenderer flag is not common in them
any longer.
We need the setter and the getter in HTMLInputElement. InputTypes use them.

BUG=342430
TEST=none; no behavior changes

Review URL: https://codereview.chromium.org/227463008

git-svn-id: svn://svn.chromium.org/blink/trunk@171026 bbb929c8-8fbe-4397-9dbb-9b2b20218538