Use gpu::Mailbox in IPCs instead of std::string

cc/texture_mailbox.cc

Index: cc/texture_mailbox.cc
diff --git a/cc/texture_mailbox.cc b/cc/texture_mailbox.cc
index b534605f77793a4583d376db2a1ea3cd4033b5cd..437fb1c9702c3d6786fe60ec1612798fd9ade6d8 100644
--- a/cc/texture_mailbox.cc
+++ b/cc/texture_mailbox.cc
@@ -12,18 +12,6 @@ TextureMailbox::TextureMailbox()
 }
 
 TextureMailbox::TextureMailbox(
-    const std::string& mailbox_name,
-    const ReleaseCallback& mailbox_callback)
-    : callback_(mailbox_callback),
-      sync_point_(0) {
-  DCHECK(mailbox_name.empty() == mailbox_callback.is_null());
-  if (!mailbox_name.empty()) {
-    CHECK(mailbox_name.size() == sizeof(name_.name));
-    name_.SetName(reinterpret_cast<const int8*>(mailbox_name.data()));
-  }
-}
-
-TextureMailbox::TextureMailbox(
     const gpu::Mailbox& mailbox_name,
     const ReleaseCallback& mailbox_callback)
     : callback_(mailbox_callback),