Begin implementing a debugger page in Observatory.

runtime/bin/vmservice/observatory/lib/src/elements/script_inset.html

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="observatory_element.html">
 
 <polymer-element name="script-inset" extends="observatory-element">
   <template>
     <style>
       .sourceInset {
-        padding-left: 15%;
-        padding-right: 15%;
       }
       .sourceBox {
-        width: 100%;
         background-color: #f5f5f5;
         border: 1px solid #ccc;
         padding: 10px;
         overflow-y: auto;
       }
       .sourceTable {
         display: table;
       }
       .sourceRow {
         display: table-row;
@@ skipping 14 matching lines @@
       }
       .hitsNotExecuted {
         background-color: #e66;
       }
       .hitsExecuted {
         background-color: #6d6;
       }
     </style>
     <div class="sourceInset">
       <content></content>
-      <div class="sourceBox" style="height:{{height}}">
+      <div class="sourceBox" style="max-height:{{height}}">
         <div class="sourceTable">
           <template if="{{ linesReady }}">
             <template repeat="{{ line in lines }}">
               <div class="sourceRow" id="{{ makeLineId(line.line) }}">
                 <breakpoint-toggle line="{{ line }}"></breakpoint-toggle>
 
                 <div class="sourceItem">&nbsp;</div>
 
                 <template if="{{ line.hits == null ||
                               line.hits < 0 }}">
@@ skipping 85 matching lines @@
     <template if="{{ line.bpt != null && line.bpt['resolved'] && !busy}}">
       <div class="resolvedBreakpoint">
         <a on-click="{{ toggleBreakpoint }}">B</a>
       </div>
     </template>
 
   </template>
 </polymer-element>
 
 <script type="application/dart" src="script_inset.dart"></script>