Make cc::SurfaceId unguessable

cc/surfaces/surface_id.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_SURFACES_SURFACE_ID_H_
 #define CC_SURFACES_SURFACE_ID_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <functional>
 
 namespace cc {
 
 struct SurfaceId {
-  SurfaceId() : id(0) {}
-  explicit SurfaceId(uint64_t id) : id(id) {}
+  SurfaceId() : id_namespace(0), id(0) {}
+  SurfaceId(uint32_t id_namespace, uint64_t id)
+      : id_namespace(id_namespace), id(id) {}
 
-  bool is_null() const { return id == 0; }
+  bool is_null() const { return id_namespace == 0 && id == 0; }
 
   // See SurfaceIdAllocator::GenerateId.
-  uint32_t id_namespace() const { return id >> 32; }
-
+  uint32_t id_namespace;
   uint64_t id;
 };
 
 inline bool operator==(const SurfaceId& a, const SurfaceId& b) {
-  return a.id == b.id;
+  return (a.id_namespace == a.id_namespace) && (a.id == b.id);
 }
 
 inline bool operator!=(const SurfaceId& a, const SurfaceId& b) {
   return !(a == b);
 }
 
 inline bool operator<(const SurfaceId& a, const SurfaceId& b) {
-  return a.id < b.id;
+  return (a.id_namespace < b.id_namespace) ||
+         (a.id_namespace == b.id_namespace && a.id < b.id);
 }
 
 struct SurfaceIdHash {
   size_t operator()(const SurfaceId& key) const {
-    return std::hash<uint64_t>()(key.id);
+    return std::hash<uint64_t>()((key.id_namespace) | (key.id << 32));

[jbauman, 2016/05/20 00:29:00]

Probably better to use base::HashInts64.

[Fady Samuel, 2016/05/20 00:40:31]

Done.

   }
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_ID_H_