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

sync/syncable/entry_kernel.cc

Index: sync/syncable/entry_kernel.cc
diff --git a/sync/syncable/entry_kernel.cc b/sync/syncable/entry_kernel.cc
index 146bbc8e811e363a11f71a94718aa960a9c3c118..7a98ae364436103d5b4aa48885441e859e051c48 100644
--- a/sync/syncable/entry_kernel.cc
+++ b/sync/syncable/entry_kernel.cc
@@ -17,7 +17,7 @@
 namespace syncer {
 namespace syncable {
 
-EntryKernel::EntryKernel() : dirty_(false) {
+EntryKernel::EntryKernel() : dirty_(false), cached_size_(0) {
   // Everything else should already be default-initialized.
   for (int i = 0; i < INT64_FIELDS_COUNT; ++i) {
     int64_fields[i] = 0;