Uber Comp: never change mailbox name associated with a texture object.

cc/transferable_resource.cc

Index: cc/transferable_resource.cc
===================================================================
--- cc/transferable_resource.cc	(revision 166046)
+++ cc/transferable_resource.cc	(working copy)
@@ -2,10 +2,28 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "base/logging.h"
 #include "cc/transferable_resource.h"
 
 namespace cc {
 
+Mailbox::Mailbox() {
+  memset(name, 0, sizeof(name));
+}
+
+bool Mailbox::isZero() const {
+  for (int i = 0; i < arraysize(name); ++i) {
+    if (name[i])
+      return false;
+  }
+  return true;
+}
+
+void Mailbox::setName(const GLbyte* n) {
+  DCHECK(isZero() || !memcmp(name, n, sizeof(name)));
+  memcpy(name, n, sizeof(name));
+}
+
 TransferableResource::TransferableResource()
     : id(0),
       format(0) {