Add a working command line debugger to Observatory.

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

Index: runtime/observatory/lib/src/elements/script_inset.html
diff --git a/runtime/observatory/lib/src/elements/script_inset.html b/runtime/observatory/lib/src/elements/script_inset.html
index fb8c2dc1892d0a580d98545afa36e4c25fcbb453..e01110a772cad62773328ec20587c269108d2c00 100644
--- a/runtime/observatory/lib/src/elements/script_inset.html
+++ b/runtime/observatory/lib/src/elements/script_inset.html
@@ -25,7 +25,10 @@
         line-height: 125%;
         white-space: pre;
       }
-      .sourceItemCurrent {
+      .currentLine {
+        background-color: #fff;
+      }
+      .currentCol {
         background-color: #6cf;
       }
       .hitsNone, .hitsNotExecuted, .hitsExecuted {
@@ -69,7 +72,13 @@
                   <div class="sourceItem">&nbsp;</div>
 
                   <template if="{{ line.line == currentLine }}">
-                    <div class="sourceItemCurrent">{{line.text}}</div>
+                    <div class="sourceItem"><span class="currentLine">{{
+                          clip(line.text,0,currentCol
+                        )}}</span><span class="currentCol">{{
+                          clip(line.text,currentCol,currentCol+1)
+                        }}</span><span class="currentLine">{{
+                          clip(line.text,currentCol+1)
+                        }}</span></div>
                   </template>
                   <template if="{{ line.line != currentLine }}">
                     <div class="sourceItem">{{line.text}}</div>