Require ::picker(select) appearance:base-select opt-in

This patch requires that not only appearance:base-select be applied to
<select> to make the popup be a popover, but also for
appearance:base-select to be applied to select::picker(select). This is
being discussed here: w3c/csswg-drafts#10440

Change-Id: Ib089a9f8a4c0bea30d2f4fb9da1df185f4272db0

Author: josepharhar

html/semantics/forms/the-select-element/stylable-select/select-accessibility-minimum-target-size.tentative.html

@@ -7,7 +7,13 @@
 <script src="/resources/testdriver.js"></script>
 <script src="/resources/testdriver-vendor.js"></script>
 
-<select style="appearance:base-select">
+<style>
+select, select::picker(select) {
+  appearance: base-select;
+}
+</style>
+
+<select>
   <option></option>
 </select>
 

html/semantics/forms/the-select-element/stylable-select/select-fallback-datalist-animations.tentative.html

@@ -8,7 +8,7 @@
 <script src="/resources/testdriver-vendor.js"></script>
 
 <style>
-select {
+select, select::picker(select) {
   appearance: base-select;
 }
 

html/semantics/forms/the-select-element/stylable-select/select-keyboard-behavior.tentative.html

@@ -11,7 +11,7 @@
 <script src="/resources/testdriver-actions.js"></script>
 
 <style>
-select {
+select, select::picker(select) {
   appearance: base-select;
 }
 </style>

html/semantics/forms/the-select-element/stylable-select/select-mouse-behavior.tentative.html

@@ -10,7 +10,7 @@
 <script src="/resources/testdriver-actions.js"></script>
 
 <style>
-select {
+select, select::picker(select) {
   appearance: base-select;
 }
 </style>

html/semantics/forms/the-select-element/stylable-select/select-option-hover-styles.tentative.html

@@ -12,10 +12,13 @@
   color: SelectedItemText;
   background-color: SelectedItem;
 }
+select, select::picker(select) {
+  appearance: base-select;
+}
 </style>
 <div id=selecteditem>SelectedItem test colors</div>
 
-<select style="appearance:base-select">
+<select>
   <option class=one>one</option>
   <option class=two>two</option>
   <option class=three disabled>disabled</option>

html/semantics/forms/the-select-element/stylable-select/selectedoption.tentative.html

@@ -6,8 +6,14 @@
 <script src="/resources/testdriver.js"></script>
 <script src="/resources/testdriver-vendor.js"></script>
 
+<style>
+select, select::picker(select) {
+  appearance: base-select;
+}
+</style>
+
 <form>
-  <select style="appearance:base-select">
+  <select>
     <button>
       <selectedoption></selectedoption>
     </button>