[WIP][tracing] Add memory dump provider for sync Directory

sync/syncable/entry_kernel.h

Index: sync/syncable/entry_kernel.h
diff --git a/sync/syncable/entry_kernel.h b/sync/syncable/entry_kernel.h
index 064cdd46b6d1e79b0b53538c6310a4a6c1ecba89..e5170eb5b9c5745ae95ee16de577fa6cdc9299c0 100644
--- a/sync/syncable/entry_kernel.h
+++ b/sync/syncable/entry_kernel.h
@@ -231,6 +231,7 @@ struct SYNC_EXPORT EntryKernel {
       dirty_index->insert(ref(META_HANDLE));
     }
     dirty_ = true;
+    cached_size_ = 0;
   }
 
   // Clear the dirty bit, and optionally remove this entry's metahandle from
@@ -248,6 +249,10 @@ struct SYNC_EXPORT EntryKernel {
     return dirty_;
   }
 
+  inline void set_cached_size(size_t size) { cached_size_ = size; }
+
+  inline size_t cached_size() const { return cached_size_; }
+
   // Setters.
   inline void put(MetahandleField field, int64_t value) {
     int64_fields[field - INT64_FIELDS_BEGIN] = value;
@@ -388,6 +393,7 @@ struct SYNC_EXPORT EntryKernel {
  private:
   // Tracks whether this entry needs to be saved to the database.
   bool dirty_;
+  size_t cached_size_;
 };
 
 class EntryKernelLessByMetaHandle {