Add find_timeouts and caching to tools/gardening

tools/gardening/lib/src/cache.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 'dart:async';
+import 'dart:io';
+
+import 'util.dart';
+
+final Cache cache = new Cache(Uri.base.resolve('temp/gardening-cache/'));
+
+/// Simple cache for test step output.
+class Cache {
+  Uri base;
+
+  Cache(this.base);
+
+  Map<String, String> memoryCache = <String, String>{};
+
+  /// Load the cache text for [path] or call [ifAbsent] to fetch the data.
+  Future<String> read(String path, Future<String> ifAbsent()) async {
+    if (memoryCache.containsKey(path)) {
+      log('Found $path in memory cache');
+      return memoryCache[path];
+    }
+    File file = new File.fromUri(base.resolve(path));
+    String text;
+    if (file.existsSync()) {
+      log('Found $path in file cache');
+      text = file.readAsStringSync();
+      memoryCache[path] = text;
+    } else {
+      log('Loading $path');
+      text = await ifAbsent();
+      write(path, text);
+    }
+    return text;
+  }
+
+  /// Store [text] as the cache data for [path].
+  void write(String path, String text) {
+    log('Creating $path in file cache');
+    File file = new File.fromUri(base.resolve(path));
+    file.createSync(recursive: true);
+    file.writeAsStringSync(text);
+    memoryCache[path] = text;
+  }
+}