Mock up code completion.

dart/site/try/index.html

Index: dart/site/try/index.html
diff --git a/dart/site/try/index.html b/dart/site/try/index.html
index 708a1c4d49c22aa94a68b2d89e6d7ee90af21835..d613145876775b64025a7f3fe7fe4f2eb7a9eb87 100644
--- a/dart/site/try/index.html
+++ b/dart/site/try/index.html
@@ -39,6 +39,26 @@ a:hover.diagnostic span {
   font-weight: bolder;
   opacity: 0.0;
 }
+
+.dart-code-completion-holder {
+  position: relative;
+}
+
+.dart-code-completion-holder *.dart-code-completion {
+  display: none;
+  position: absolute;
+  left: 0px;
+  right: 0px;
+  min-width: 400px;
+  background: white;
+  foreground: black;
+  border: 1px solid black;
+  z-index: 10;
+}
+
+.dart-code-completion-holder.active *.dart-code-completion {
+  display: block;
+}
 </style>
 
 <meta itemprop="name" content="Try Dart!">