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

content/renderer/browser_plugin/browser_plugin.h

Index: content/renderer/browser_plugin/browser_plugin.h
diff --git a/content/renderer/browser_plugin/browser_plugin.h b/content/renderer/browser_plugin/browser_plugin.h
index cd8f01368a3662e61d4ec4837135a19fda4cdf2b..40136d4472e50af44150e2608bcdf64cfd0fcb6b 100644
--- a/content/renderer/browser_plugin/browser_plugin.h
+++ b/content/renderer/browser_plugin/browser_plugin.h
@@ -26,6 +26,10 @@ struct BrowserPluginHostMsg_ResizeGuest_Params;
 struct BrowserPluginMsg_LoadCommit_Params;
 struct BrowserPluginMsg_UpdateRect_Params;
 
+namespace gpu {
+struct Mailbox;
+}
+
 namespace content {
 
 class BrowserPluginCompositingHelper;
@@ -313,7 +317,7 @@ class CONTENT_EXPORT BrowserPlugin :
   void OnAdvanceFocus(int instance_id, bool reverse);
   void OnBuffersSwapped(int instance_id,
                         const gfx::Size& size,
-                        std::string mailbox_name,
+                        gpu::Mailbox mailbox_name,
                         int gpu_route_id,
                         int gpu_host_id);
   void OnGuestContentWindowReady(int instance_id,