sync: Re-implement getAllNodes WebUI function

sync/engine/directory_type_debug_info_emitter.h

Index: sync/engine/directory_type_debug_info_emitter.h
diff --git a/sync/engine/directory_type_debug_info_emitter.h b/sync/engine/directory_type_debug_info_emitter.h
new file mode 100644
index 0000000000000000000000000000000000000000..4cee24672261f9fcc1ec7b592b0739539a94f829
--- /dev/null
+++ b/sync/engine/directory_type_debug_info_emitter.h
@@ -0,0 +1,34 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SYNC_ENGINE_DIRECTORY_TYPE_DEBUG_INFO_EMITTER_H_
+#define SYNC_ENGINE_DIRECTORY_TYPE_DEBUG_INFO_EMITTER_H_
+
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/values.h"
+#include "sync/syncable/directory.h"
+
+namespace syncer {
+
+// Suports debugging requests for a certain directory type.

[Nicolas Zea, 2014/04/04 23:01:27]

Why only for one type? It seems more efficient to have it be capable of handler
a full ModelTypeSet?

[rlarocque, 2014/04/05 00:07:27]

I'm hoping this pattern of one object per type will turn out to be useful in the
future.  This class will be reused to implement per-type application counts,
commit counts, etc.

I suppose we could make a special case for GetAllNodes(), but the efficiency
difference isn't all that great.  The really expensive part of this operation is
serialization.  Iterating over the directory 20+ times is a drop in the bucket
compared to that cost.  Besides, we only need to pay this cost when we're
debugging, so it's not something I'm inclined to optimize very much.

+class DirectoryTypeDebugInfoEmitter {
+ public:
+  DirectoryTypeDebugInfoEmitter(syncable::Directory* directory,
+                                syncer::ModelType type);
+  virtual ~DirectoryTypeDebugInfoEmitter();
+
+  // Returns a ListValue representation of all known nodes of this type.
+  scoped_ptr<base::ListValue> GetAllNodes();
+
+ private:
+  syncable::Directory* directory_;
+  ModelType type_;
+
+  DISALLOW_COPY_AND_ASSIGN(DirectoryTypeDebugInfoEmitter);
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_ENGINE_DIRECTORY_TYPE_DEBUG_INFO_EMITTER_H_