Merge "INPUT/TEXTAREA elements: Fix incorrect selectionStart/selectionEnd values after blur." to M59

We failed to update selectionStart/selectionEnd cache because
TextControlElement::SelectionChanged() is not called in some cases after
crrev.com/450370.

After this CL, selection values are cached in webkitEditableContentChanged event
handling code too.  It is called on every DOM mutation in text control editor.

BUG=714425

Review-Url: https://codereview.chromium.org/2878613002
Cr-Original-Commit-Position: refs/heads/master@{#471290}
Review-Url: https://codereview.chromium.org/2882953002 .
Cr-Commit-Position: refs/branch-heads/3071@{#549}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
3 files changed