gpu: Generate mailboxes on client side

gpu/command_buffer/common/mailbox.cc

 // Copyright 2013 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.
 
 #include "gpu/command_buffer/common/mailbox.h"
 
 #include <string.h>
 
 #include "base/logging.h"
+#include "crypto/random.h"
 
 namespace gpu {
 
 Mailbox::Mailbox() {
   memset(name, 0, sizeof(name));
 }
 
 bool Mailbox::IsZero() const {
   for (size_t i = 0; i < arraysize(name); ++i) {
     if (name[i])
       return false;
   }
   return true;
 }
 
 void Mailbox::SetZero() {
   memset(name, 0, sizeof(name));
 }
 
 void Mailbox::SetName(const int8* n) {
   DCHECK(IsZero() || !memcmp(name, n, sizeof(name)));
   memcpy(name, n, sizeof(name));
 }
 
+Mailbox Mailbox::Generate() {
+  Mailbox result;
+  crypto::RandBytes(result.name, sizeof(result.name));
+#if !defined(NDEBUG)
+  int8 value = 1;
+  for (size_t i = 1; i < sizeof(result.name); ++i)
+    value ^= result.name[i];
+  result.name[0] = value;
+#endif
+  return result;
+}
+
+bool Mailbox::Verify() const {
+#if !defined(NDEBUG)
+  int8 value = 1;
+  for (size_t i = 0; i < sizeof(name); ++i)
+    value ^= name[i];
+  return value == 0;
+#else
+  return true;
+#endif
+}
+
 }  // namespace gpu