Use timeout to read most recent build from http

tools/gardening/lib/src/client.dart

Index: tools/gardening/lib/src/client.dart
diff --git a/tools/gardening/lib/src/client.dart b/tools/gardening/lib/src/client.dart
index f73a50df5efdeb18501806c07e42d9c9ad58c9f5..95424fb72ca195613d68b57589845c315abcad66 100644
--- a/tools/gardening/lib/src/client.dart
+++ b/tools/gardening/lib/src/client.dart
@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
+import 'dart:async' hide TimeoutException;
 import 'dart:io' hide HttpException;
 
 import 'buildbot_data.dart';
@@ -28,16 +28,40 @@ class HttpBuildbotClient implements BuildbotClient {
 
   @override
   Future<BuildResult> readResult(BuildUri buildUri) async {
-    try {
-      return await readBuildResultFromHttp(_client, buildUri);
-    } on HttpException {
-      return null;
-    } on SocketException {
-      return null;
+    Duration timeout;
+    if (buildUri.buildNumber < 0) {
+      timeout = new Duration(seconds: 1);
+    }
+
+    void skipToPreviousBuildNumber() {
+      BuildUri prevBuildUri = buildUri.prev();
+      log('Skip build number '
+          '${buildUri.buildNumber} -> ${prevBuildUri.buildNumber}');
+      buildUri = buildUri.prev();
+    }
+
+    while (true) {
+      try {
+        return await readBuildResultFromHttp(_client, buildUri, timeout);
+      } on TimeoutException {
+        if (timeout != null) {
+          skipToPreviousBuildNumber();
+          continue;
+        }
+        return null;
+      } on HttpException {
+        if (timeout != null) {
+          skipToPreviousBuildNumber();
+          continue;
+        }
+        return null;
+      } on SocketException {
+        return null;
+      }
     }
   }
 
-  int get mostRecentBuildNumber => -2;
+  int get mostRecentBuildNumber => -1;
 
   @override
   void close() {