Move Mailbox from cc to gpu, and its traits to gpu/ipc

cc/transferable_resource.cc

Index: cc/transferable_resource.cc
diff --git a/cc/transferable_resource.cc b/cc/transferable_resource.cc
index 886b4423ec09a617e126db31fc4784b6e4162cd5..ce26434bca4a4c889509590a1d56c62970d9141e 100644
--- a/cc/transferable_resource.cc
+++ b/cc/transferable_resource.cc
@@ -7,23 +7,6 @@
 
 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 int8* n) {
-  DCHECK(isZero() || !memcmp(name, n, sizeof(name)));
-  memcpy(name, n, sizeof(name));
-}
-
 TransferableResource::TransferableResource()
     : id(0),
       sync_point(0),