[Sync] Add support for loading, updating and querying delete journals in

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 6dc88a78198664e3a5e9ad186e43fe6e73c173ef..e9cf828a59454384e922b3d9762759418754a732 100644
--- a/sync/syncable/entry_kernel.h
+++ b/sync/syncable/entry_kernel.h
@@ -5,6 +5,8 @@
 #ifndef SYNC_SYNCABLE_ENTRY_KERNEL_H_
 #define SYNC_SYNCABLE_ENTRY_KERNEL_H_
 
+#include <set>
+
 #include "base/time.h"
 #include "base/values.h"
 #include "sync/base/sync_export.h"
@@ -323,6 +325,17 @@ struct SYNC_EXPORT_PRIVATE EntryKernel {
   bool dirty_;
 };
 
+class EntryKernelLessByMetaHandle {
+ public:
+  inline bool operator()(const EntryKernel* a,
+                         const EntryKernel* b) const {
+    return a->ref(META_HANDLE) < b->ref(META_HANDLE);
+  }
+};
+
+typedef std::set<const EntryKernel*, EntryKernelLessByMetaHandle>
+    EntryKernelSet;
+
 struct EntryKernelMutation {
   EntryKernel original, mutated;
 };