Change event should not be dispatched by clicking a scrollbar of listbox <select>.

We fixed crbug.com/244406, but the fix was incomplete.

Bug detail:
If the size of option list is changed after the last 'change' event and
'mouseup' happens on the scrollbar, new 'change' event is dispatched even though
the selection state is not changed.
HTMLSelectElement::listBoxOnChange dispatches 'change' event if
m_lastOnChangeSelection.size() is different from the option list size. (Why?)

How to fix:
When the option list size is changed, we should update m_lastOnChangeSelection
so that it represents reality or should avoid to call listBoxOnChange() in
mouseup event handler. This patch implements the latter by clearing
m_lastOnChangeSelection.

BUG=252559
TEST=automated

Review URL: https://chromiumcodereview.appspot.com/17514006

git-svn-id: svn://svn.chromium.org/blink/trunk@152868 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Improve contenteditable accessibility notifications.

We want a contentEditable region or an element with role=textbox to
behave the same as an <input> or <textarea> for assistive technology
when the user is typing - it should send both a "value changed"
notification and a "selected text changed" (really means "selection
changed") on the node playing the role of the text box.

The logic was wrong in a few places. This cleans it up and fixes it,
and adds a new test.

BUG=251638
R=dtseng@chromium.org

Review URL: https://codereview.chromium.org/17381014

git-svn-id: svn://svn.chromium.org/blink/trunk@152870 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Rebaseline remaining Mac results after SK_IGNORE_MAC_TEXT_BOUNDS_FIX removal.

BUG=252414
TBR=steveblock@chromium.org

git-svn-id: svn://svn.chromium.org/blink/trunk@152871 bbb929c8-8fbe-4397-9dbb-9b2b20218538