Teach window.location.href setter to handle relative urls.

sky/examples/raw/touch-demo.sky

 #!mojo mojo:sky_viewer
 <sky>
 <import src="/sky/framework/debug/shake-to-reload.sky" />
 <style>
 dot {
     position: absolute;
     height: 10px;
     width: 10px;
     background-color: #00FF00;
     border-radius: 5px;
     opacity: .75;
 }
 
 log {
+    display: paragraph;
     margin-top: 50px;
 }
 </style>
 <log>Touch the screen!</log>
 <script>
 import "dart:sky";
 
 // Material design colors. :p
 List<String> colors = [
   "#009688",
@@ skipping 35 matching lines @@
 }
 
 void main() {
   document.addEventListener("pointerdown", moreDots);
   document.addEventListener("pointermove", runToTheCenter);
   document.addEventListener("pointerup", goAway);
   document.addEventListener("pointercancel", stopDots);
 }
 </script>
 </sky>