cc: Allow pepper to avoid DCHECK but reuse gpu::Mailbox.

cc/layers/texture_layer.cc

 // Copyright 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/texture_layer.h"
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/location.h"
 #include "base/synchronization/lock.h"
@@ skipping 117 matching lines @@
   texture_id_ = id;
   SetNeedsCommit();
   // The texture id needs to be removed from the active tree before the
   // commit is called complete.
   SetNextCommitWaitsForActivation();
 }
 
 void TextureLayer::SetTextureMailboxInternal(
     const TextureMailbox& mailbox,
     scoped_ptr<SingleReleaseCallback> release_callback,
-    bool requires_commit) {
+    bool requires_commit,
+    bool allow_mailbox_reuse) {
   DCHECK(uses_mailbox_);
   DCHECK(!mailbox.IsValid() || !holder_ref_ ||
-         !mailbox.Equals(holder_ref_->holder()->mailbox()));
+         !mailbox.Equals(holder_ref_->holder()->mailbox()) ||
+         allow_mailbox_reuse);
   DCHECK_EQ(mailbox.IsValid(), !!release_callback);
 
   // If we never commited the mailbox, we need to release it here.
   if (mailbox.IsValid()) {
     holder_ref_ =
         TextureMailboxHolder::Create(mailbox, release_callback.Pass());
   } else {
     holder_ref_.reset();
   }
   needs_set_mailbox_ = true;
   // If we are within a commit, no need to do it again immediately after.
   if (requires_commit)
     SetNeedsCommit();
   else
     SetNeedsPushProperties();
 
   // The active frame needs to be replaced and the mailbox returned before the
   // commit is called complete.
   SetNextCommitWaitsForActivation();
 }
 
 void TextureLayer::SetTextureMailbox(
     const TextureMailbox& mailbox,
     scoped_ptr<SingleReleaseCallback> release_callback) {
+  bool requires_commit = true;
+  bool allow_mailbox_reuse = false;
   SetTextureMailboxInternal(
-      mailbox,
-      release_callback.Pass(),
-      true /* requires_commit */);
+      mailbox, release_callback.Pass(), requires_commit, allow_mailbox_reuse);
+}
+
+static void IgnoreReleaseCallback(uint32 sync_point, bool lost) {}
+
+void TextureLayer::SetTextureMailboxWithoutReleaseCallback(
+    const TextureMailbox& mailbox) {
+  // We allow reuse of the mailbox if there is a new sync point signalling new
+  // content, and the release callback goes nowhere since we'll be calling it
+  // multiple times for the same mailbox.
+  DCHECK(!mailbox.IsValid() || !holder_ref_ ||
+         !mailbox.Equals(holder_ref_->holder()->mailbox()) ||
+         mailbox.sync_point() != holder_ref_->holder()->mailbox().sync_point());
+  scoped_ptr<SingleReleaseCallback> release;
+  bool requires_commit = true;
+  bool allow_mailbox_reuse = true;
+  if (mailbox.IsValid())
+    release = SingleReleaseCallback::Create(base::Bind(&IgnoreReleaseCallback));
+  SetTextureMailboxInternal(
+      mailbox, release.Pass(), requires_commit, allow_mailbox_reuse);
 }
 
 void TextureLayer::WillModifyTexture() {
   if (!uses_mailbox_ && layer_tree_host() && (DrawsContent() ||
       content_committed_)) {
     layer_tree_host()->AcquireLayerTextures();
     content_committed_ = false;
   }
 }
 
@@ skipping 41 matching lines @@
   bool updated = Layer::Update(queue, occlusion);
   if (client_) {
     if (uses_mailbox_) {
       TextureMailbox mailbox;
       scoped_ptr<SingleReleaseCallback> release_callback;
       if (client_->PrepareTextureMailbox(
               &mailbox,
               &release_callback,
               layer_tree_host()->UsingSharedMemoryResources())) {
         // Already within a commit, no need to do another one immediately.
-        SetTextureMailboxInternal(
-            mailbox,
-            release_callback.Pass(),
-            false /* requires_commit */);
+        bool requires_commit = false;
+        bool allow_mailbox_reuse = false;
+        SetTextureMailboxInternal(mailbox,
+                                  release_callback.Pass(),
+                                  requires_commit,
+                                  allow_mailbox_reuse);
         updated = true;
       }
     } else {
       texture_id_ = client_->PrepareTexture();
       updated = true;
       SetNeedsPushProperties();
       // The texture id needs to be removed from the active tree before the
       // commit is called complete.
       SetNextCommitWaitsForActivation();
     }
@@ skipping 106 matching lines @@
 
 void TextureLayer::TextureMailboxHolder::ReturnAndReleaseOnImplThread(
     uint32 sync_point,
     bool is_lost) {
   Return(sync_point, is_lost);
   message_loop_->PostTask(
       FROM_HERE, base::Bind(&TextureMailboxHolder::InternalRelease, this));
 }
 
 }  // namespace cc