added a timeout of 500 milliseconds.

client/lib/search.dart

 /**
  * A library for searching and filtering documentation.
  * 
  * Given a search query, a set of ranked results is created to determine the
  * best member to match that query. Priority is given in the following order:
  * library, class, typedef, and class member or top-level library member. 
  * Results with matches in the last section of their qualified names are
  * given a higher rank than those with matches in inner members of the
  * qualified name. 
  */
 library search;
 
+import 'dart:async';
+import 'package:web_ui/web_ui.dart';
+
 /** Search Index */
 Map<String, String> index = {};
 
+/** Search query. */
+@observable String searchQuery = "";
+
 class SearchResult implements Comparable {
 
   /** Qualified name of this search result references. */
   String element;
   
   /** This element's member type. */
   String type;
 
   /** Score of the search result match. Higher is better. */
   int score;
@@ skipping 22 matching lines @@
   'constructor' : 4
 };
 
 /**
  * Returns a list of up to [maxResults] number of [SearchResult]s based off the
  * searchQuery. 
  * 
  * A score is given to each potential search result based off how likely it is
  * the appropriate qualified name to return for the search query. 
  */
-List<SearchResult> lookupSearchResults(String searchQuery, int maxResults) {
-
+List<SearchResult> lookupSearchResults(String query, int maxResults) {  
+  
+  var stopwatch = new Stopwatch()..start();
+  
   var scoredResults = <SearchResult>[];
   var resultSet = new Set<String>();
-  var queryList = searchQuery.trim().toLowerCase().split(' ');
+  var queryList = query.trim().toLowerCase().split(' ');
   queryList.forEach((q) => resultSet.addAll(index.keys.where((e) =>
     e.toLowerCase().contains(q))));
   
-  for (var r in resultSet) {
+  for (var r in resultSet) {    
+    /// If it is taking too long to compute the search results, time out and
+    /// return an empty list of results.
+    if (stopwatch.elapsedMilliseconds > 500) {
+      return [];
+    }
     int score = 0;
     var lowerCaseResult = r.toLowerCase();
     var type = index[r];
     
     var splitDotQueries = [];
     // If the search was for a named constructor (Map.fromIterable), give it a
     // score boost of 200. 
     queryList.forEach((q) {
       if (q.contains('.') && lowerCaseResult.endsWith(q)) {
         score += 100;
@@ skipping 39 matching lines @@
       }
       
       // If the result item is part of the dart library, give it a small boost.
       if (qualifiedNameParts.first == 'dart') {
         score += 50;
       }
     });
     scoredResults.add(new SearchResult(r, type, score));
   }
   
+  /// If it is taking too long to compute the search results, time out and
+  /// return an empty list of results.
+  if (stopwatch.elapsedMilliseconds > 500) {
+    return [];
+  }
   scoredResults.sort();
   updatePositions(scoredResults);
   if (scoredResults.length > maxResults) {
     return scoredResults.take(maxResults).toList();
   } else {
     return scoredResults;
   } 
 }
 
 void updatePositions(List<SearchResult> list) {
   for(int i = 0; i < list.length; i++) {
     list[i].position = i;
   }
-}
+}