Make cc::SurfaceId unguessable

cc/surfaces/surface_id_allocator.h

Index: cc/surfaces/surface_id_allocator.h
diff --git a/cc/surfaces/surface_id_allocator.h b/cc/surfaces/surface_id_allocator.h
index b0f8bf42b8c2d4b62f73b4bd3e385504a5725060..fc198b680470ba777258a8b7451a5055d014099e 100644
--- a/cc/surfaces/surface_id_allocator.h
+++ b/cc/surfaces/surface_id_allocator.h
@@ -25,8 +25,6 @@ class CC_SURFACES_EXPORT SurfaceIdAllocator {
 
   SurfaceId GenerateId();
 
-  static uint32_t NamespaceForId(SurfaceId id);
-
   // This needs to be called before any sequences with this allocator's
   // namespace will be used to enforce destruction dependencies.
   // When this SurfaceIdAllocator is destroyed, its namespace is
@@ -39,7 +37,7 @@ class CC_SURFACES_EXPORT SurfaceIdAllocator {
 
  private:
   const uint32_t id_namespace_;
-  uint32_t next_id_;
+  uint64_t next_id_;
   SurfaceManager* manager_;
 
   DISALLOW_COPY_AND_ASSIGN(SurfaceIdAllocator);