Changed DB to store node positions as Ordinals.

sync/internal_api/public/base/ordinal.h

Index: sync/internal_api/public/base/ordinal.h
diff --git a/sync/internal_api/public/base/ordinal.h b/sync/internal_api/public/base/ordinal.h
index 91897599e782efda44c6854ee11bfbe31dabf3da..aa6ffa91fcf92b96015fc369e8a45bbef56dcb0b 100644
--- a/sync/internal_api/public/base/ordinal.h
+++ b/sync/internal_api/public/base/ordinal.h
@@ -78,7 +78,7 @@ class Ordinal {
   // may be valid or invalid.
   explicit Ordinal(const std::string& bytes);
 
-  // Creates an invalid Ordinal.
+  // Creates a valid initial Ordinal.
   Ordinal();
 
   // Creates a valid initial Ordinal. This is called to create the first
@@ -232,7 +232,11 @@ Ordinal<Traits>::Ordinal(const std::string& bytes)
       is_valid_(IsValidOrdinalBytes(bytes_)) {}
 
 template <typename Traits>
-Ordinal<Traits>::Ordinal() : is_valid_(false) {}
+Ordinal<Traits>::Ordinal()
+    : bytes_(Traits::kMinLength, kZeroDigit),
+      is_valid_(true){
+  bytes_[0] = kMidDigit;
+}
 
 template <typename Traits>
 Ordinal<Traits> Ordinal<Traits>::CreateInitialOrdinal() {