Implement ::placeholder CSS selector.

third_party/WebKit/LayoutTests/fast/forms/textarea/textarea-placeholder-pseudo-style.html

 <style>
 textarea.red::-webkit-input-placeholder {
     color: rgb(100, 0, 0);
 }
+
+.blue::placeholder {
+    color: blue;
+    font-weight: bold;
+    font-size: larger;
+}
+
+.prefixed-unprefixed::-webkit-input-placeholder {
+    color: red;
+}
+.prefixed-unprefixed::placeholder {
+    color: blue;
+}
+
+.unprefixed-prefixed::placeholder {
+    color: blue;
+}
+.unprefixed-prefixed::-webkit-input-placeholder {
+    color: red;
+}
 </style>
-This tests that you can set the placeholder text color.<br>
+This tests that you can set the placeholder text color.
+
+<div>
+Default style:
+<textarea placeholder="default"></textarea>
+<textarea disabled placeholder="default disabled"></textarea>
+</div>
+
+<div>
+::-webkit-input-placeholder:
 <textarea class="red" placeholder="text"></textarea>
 <textarea class="red" disabled placeholder="disabled text"></textarea>
-<textarea placeholder="default"></textarea>
-<textarea disabled placeholder="default disabled"></textarea>
+</div>
+
+<div>
+::placeholder:
+<textarea class="blue" placeholder="text"></textarea>
+<textarea class="blue" disabled placeholder="disabled text"></textarea>
+</div>
+
+<div>
+Both:
+<textarea class="prefixed-unprefixed" placeholder="unprefixed"></textarea>
+<textarea class="unprefixed-prefixed" placeholder="prefixed"></textarea>
+</div>