Add BuildBotClient to abstract http/logdog access

tools/gardening/lib/src/buildbot_structures.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // 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 'util.dart';
 
 /// The [Uri] of a build step stdio log split into its subparts.
 class BuildUri {
   final String scheme;
   final String host;
   final String prefix;
   final String botName;
   final int buildNumber;
   final String stepName;
   final String suffix;
 
   factory BuildUri(Uri uri) {
-    List<String> parts =
-        split(uri.path, ['/builders/', '/builds/', '/steps/', '/logs/']);
+    List<String> parts = split(Uri.decodeFull(uri.path),
+        ['/builders/', '/builds/', '/steps/', '/logs/']);
     String botName = parts[1];
     int buildNumber = int.parse(parts[2]);
     String stepName = parts[3];
     return new BuildUri.fromData(botName, buildNumber, stepName);
   }
 
   factory BuildUri.fromData(String botName, int buildNumber, String stepName) {
     return new BuildUri.internal('https', 'build.chromium.org',
         '/p/client.dart', botName, buildNumber, stepName, 'stdio/text');
   }
 
   BuildUri.internal(this.scheme, this.host, this.prefix, this.botName,
       this.buildNumber, this.stepName, this.suffix);
 
   BuildUri withBuildNumber(int buildNumber) {
     return new BuildUri.fromData(botName, buildNumber, stepName);
   }
 
+  int get absoluteBuildNumber => buildNumber >= 0 ? buildNumber : null;
+
   String get shortBuildName => '$botName/$stepName';
 
   String get buildName =>
       '/builders/$botName/builds/$buildNumber/steps/$stepName';
 
   String get path => '$prefix$buildName/logs/$suffix';
 
   /// Returns the path used in logdog for this build uri.
   ///
   /// Since logdog only supports absolute build numbers, [buildNumber] must be
@@ skipping 171 matching lines @@
 
 /// The result of a single test for a single test step.
 class TestStatus {
   final TestConfiguration config;
   final String status;
 
   TestStatus(this.config, this.status);
 
   String toString() => '$config: $status';
 }