INPUT element: Do not update selectionStart/selectionEnd on |value| IDL setter if the new value is same as the old value.

The HTML standard was updated recently to clarify this behavior.
The new behavior matches to TEXTAREA element, and Firefox 55.

BUG=712352

Review-Url: https://codereview.chromium.org/2884603002
Cr-Commit-Position: refs/heads/master@{#472028}
3 files changed