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

cc/texture_layer_unittest.cc

Index: cc/texture_layer_unittest.cc
diff --git a/cc/texture_layer_unittest.cc b/cc/texture_layer_unittest.cc
index 6aaf45957c571b774a07cf83cdd3984417ee99c0..7ebdac6cd89c3fc397088c8d7d2eefa3a4ee5890 100644
--- a/cc/texture_layer_unittest.cc
+++ b/cc/texture_layer_unittest.cc
@@ -293,8 +293,10 @@ public:
     }
 
     void setMailbox(char mailbox_char) {
+        gpu::Mailbox name;
+        memset(name.name, mailbox_char, sizeof(name.name));
         TextureMailbox mailbox(
-            std::string(64, mailbox_char),
+            name,
             base::Bind(
                 &TextureLayerImplWithMailboxThreadedCallback::releaseCallback,
                 base::Unretained(this)));