Revert 171569 as it broke some browser_tests on win_aura.

gpu/command_buffer/service/mailbox_manager.h

Index: gpu/command_buffer/service/mailbox_manager.h
===================================================================
--- gpu/command_buffer/service/mailbox_manager.h	(revision 171661)
+++ gpu/command_buffer/service/mailbox_manager.h	(working copy)
@@ -30,8 +30,7 @@
 // Identifies a mailbox where a texture definition can be stored for
 // transferring textures between contexts that are not in the same context
 // group. It is a random key signed with a hash of a private key.
-struct GPU_EXPORT MailboxName {
-  MailboxName();
+struct MailboxName {
   GLbyte key[GL_MAILBOX_SIZE_CHROMIUM / 2];
   GLbyte signature[GL_MAILBOX_SIZE_CHROMIUM / 2];
 };