Add gpu::MailboxHolder to hold state for a gpu::Mailbox

content/common/gpu/client/gl_helper.cc

Index: content/common/gpu/client/gl_helper.cc
diff --git a/content/common/gpu/client/gl_helper.cc b/content/common/gpu/client/gl_helper.cc
index 3ea2557a69dbb970af8e6b656a62001b30e82d50..604de8ac3f7bc6d0d981c4753b7c3e0c18e4d0e4 100644
--- a/content/common/gpu/client/gl_helper.cc
+++ b/content/common/gpu/client/gl_helper.cc
@@ -706,19 +706,17 @@ void GLHelper::WaitSyncPoint(uint32 sync_point) {
   context_->waitSyncPoint(sync_point);
 }
 
-gpu::Mailbox GLHelper::ProduceMailboxFromTexture(blink::WebGLId texture_id,
-                                                 uint32* sync_point) {
+gpu::MailboxHolder GLHelper::ProduceMailboxHolderFromTexture(
+    blink::WebGLId texture_id) {
   gpu::Mailbox mailbox;
   context_->genMailboxCHROMIUM(mailbox.name);
-  if (mailbox.IsZero()) {
-    *sync_point = 0;
-    return mailbox;
-  }
+  if (mailbox.IsZero())
+    return gpu::MailboxHolder();
   content::ScopedTextureBinder<GL_TEXTURE_2D> texture_binder(context_,
                                                              texture_id);
   context_->produceTextureCHROMIUM(GL_TEXTURE_2D, mailbox.name);
-  *sync_point = context_->insertSyncPoint();
-  return mailbox;
+  return gpu::MailboxHolder(
+      mailbox, GL_TEXTURE_2D, context_->insertSyncPoint());
 }
 
 blink::WebGLId GLHelper::ConsumeMailboxToTexture(const gpu::Mailbox& mailbox,