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>
 
+#include "base/hash.h"
+
 namespace cc {
 
 struct SurfaceId {
-  SurfaceId() : id(0) {}
-  explicit SurfaceId(uint64_t id) : id(id) {}
+  SurfaceId() : id_namespace(0), local_id(0) {}
+  SurfaceId(const SurfaceId& other)
+      : id_namespace(other.id_namespace), local_id(other.local_id) {}
+  SurfaceId(uint32_t id_namespace, uint64_t local_id)
+      : id_namespace(id_namespace), local_id(local_id) {}
 
-  bool is_null() const { return id == 0; }
+  bool is_null() const { return id_namespace == 0 && local_id == 0; }
 
   // See SurfaceIdAllocator::GenerateId.
-  uint32_t id_namespace() const { return id >> 32; }
-
-  uint64_t id;
+  uint32_t id_namespace;
+  uint64_t local_id;
 };
 
 inline bool operator==(const SurfaceId& a, const SurfaceId& b) {
-  return a.id == b.id;
+  return (a.id_namespace == b.id_namespace) && (a.local_id == b.local_id);

[Tom Sepez, 2016/05/20 20:22:02]

nit: overparenthesized, also line 40

[Fady Samuel, 2016/05/24 20:33:07]

Done. I've switched to if statements for readability. I can never remember the
order of operations and I always have to think about it if I don't see parens. 

 }
 
 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.local_id < b.local_id));
 }
 
 struct SurfaceIdHash {
   size_t operator()(const SurfaceId& key) const {
-    return std::hash<uint64_t>()(key.id);
+    return base::HashInts64(key.id_namespace, key.local_id);

[danakj, 2016/05/20 21:01:36]

Just use HashInts() it picks the right function.

[Fady Samuel, 2016/05/24 20:33:07]

Done.

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