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This is a reland of a98ef426
Differences from the original CL:
 * Add aria-hidden="true" to the shadow element because AXMenuList
   assumes its child is only AXMenuListPopup.
   This fixes ChromeVox test failures with the original CL.

Original change's description:
> Change the anonymous block in LayoutMenuList to a shadow element
>
> Enable rendering of the shadow element of <select>, and remove anonymous
> block in LayoutMenuList.
>
> * HTMLOptionElement::ParseAttribute():
>   Update the shadow element content on option[label] change.
>
> * HTMLSelectElement::UpdateFromElement():
>   Fold LayoutMenuList::UpdateFromElement() into here. If option_style_
>   and InnerElemnet's style are inconsistent, update InnerElement's
>   style.
>
> * HTMLSelectElement::UpdateMenuListLabel()
>   Move the code in LayoutMenuList::UpdateInnerStyle() here.
>   Also, kick TextChanged ax notification which LayoutText::ForceSetText
>   did.
>
> * MenuListInnerElement::CustomStyleForLayoutObject():
>   Set "display: block"
>   Add custom style which the anonymous block used.
>
> * layout_menu_list.{h,cc}:
>   Remove a lot of code.
>
> * ax_layout_object_test.cc:
>   Add tests to check if AXLayoutObject::StringValue() respects to
>   text-transform and -webkit-text-security.
>
> * web_tests/accessibility/notification-listeners.html:
>   Remove TextChanged notification expectation. After this CL, <select>
>   won't notify TextChanged in this test scenario. The text is changed
>   before creating LayoutObject and AXLayoutObject.
>
>
>
> Bug: 1040828
> Change-Id: Ia0c19f0897ab2d1461e457c83adceda2c0739f9f
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2024250
> Reviewed-by: Koji Ishii <kojii@chromium.org>
> Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
> Commit-Queue: Kent Tamura <tkent@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#738416}

Bug: 1040828
Change-Id: I9696527720316c861b657a03e0a1ed9cfa7db653
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2040631Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738834}